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Full text of "A treatise on the common sole (Solea vulgaris), considered both as an organism and as a commodity"

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A TREATISE ON 



THE COMMON SOLE 

(SOLEA VULGARIS), 
CONSIDERED BOTH AS AN ORGANISM AND AS A C0M3I0DITY.. 



PREPARED FOR THE 



MAKIXE BIOLOGICAL ASSOCTATIOX OF THE UNITED KINGDOM 



J. T. CUNNINGHAM, M.A., F.R.S.E. 

' — 

Lain Fellow of Vnircr-nty College, Oxford; Natural ixt to the Association. / 







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TLrMOUTH 



PUBLISHED BY THE ASSOCIATION. 



1890. 



LONDON : 

UAmtlSOX AND SONS, PRINTEliS IN ORDINAnV TO nKi; MAJKSTV, 

ST. MARI'IN's LAXK. 



COIS^TENTS. 



Page 
Preface \- 



PART I. 

T A X N M 1 t A 1,. 

Chapter 1, — Classification of the Flat-fishes 3 

Chapter 2. — History of the Genus Solea 11 

Chapter 3. — Solea vulgaris, Quensel 15 

Chapter -l. — Solea lascaris, Bonaparte 20 

Chapter 5. — Solea variegata, Fleming (Donovan) 25 

Chapter 6. — Solea lutea, Bonaparte 29 

Chapter 7. — Solea Greenii, Giinthei' 32 



PART II, 

iloKPHOLOGICAL. 

Chaftek 1. — The Osseous Skeleton 35 

The Skull 35 

The Vertebral Coluum • . 38 

The Jaws and Branchial Arches 41 

Chapter 2. — The Fibrous Membranes and Musculature 45 

The Fibrous Membranes 45 

The Musculiitux-e 46 

Chapter 3. — The Viscera, and Vascular System 64 

The Viscera, female 54 

Ditto, male 66 

Minute Structure of the Reproductive Organs, and Develojiment of the 

Reproductive Elements 69 

The Vasjular System 64 

A 2 



IV 

Page 

Chapter 4. — The Nervous Sj-stem t>G 

The Brain GG 

The Cranial Nerves G8 

Chapter 5.— The Skin 73 

Dermal Canals and Sense Organs 74 

Minute Stracture of the Skin, Dermal Tubes, and Sense Organs .... 79 

Chapter 6. — Embryology 84 

Chapter 7. — Structni-e of Phylhmdla solece 93 



PART III. 

B 1 N M I C a L. 

Chapter 1. — Geographical Distribntion 99 

Chaiteb 2.— Habits, Food, &c 101 

Food 105 

Parasites 108 

Enemies 109 

Chapter 3.— Colour 110 

Chapter 4. — Breeding 114 

Chapter 5. — Development and Growth 119 

PART IV. 

E C N M I C A r,. 

Chapter 1. — Artificial Propagation 129 

Chaitkr 2.— The Sole Fishery 137 

Chapter 3. — Pi-actical Measures 142 



PREFACE. 



The distinction between theory and practice is one that is generally recognised in all 
departments of human affairs. By theory in this context is meant pure knowledge — 
the knowledge of things as they are apart from any use which may be made of the 
knowledge. This kind of knowledge — the result of the most careful investigation, 
continually corrected by improved experiments and more widely extended observation, 
and subjected to the most rigid criticism by successive generations of enquirers — is 
pure science. Practice, on the other hand, or practical knowledge, is the knowledge 
of the methods by which the material and the forces of nature can be made to 
satisfy human needs and desires. Practice necessarily depends on some knowledge 
of the properties and relations of natural objects and forces, though in many cases 
it may simply consist in knowing that a certain desired result will generally be 
produced by particular operations. This is the kind of knowledge possessed by 
men trained and experienced in particular " trades " or crafts. 

The distinction has existed since the very commencement of human civilisation. 
The earliest representatives of humanity, like the most primitive savages now existing, 
had some knowledge of their surroundings which was not directly useful to them, while 
they understood very little the arts which they practised. To some extent the develop- 
ment of pure science and that of practical science have proceeded independently, but to 
a large extent they have influenced one another. Practical science has often received s 
great impetus from the discoveries of abstract inquiry, and pure science has often made 
enormous strides by the study of the results exhibited by industrial processes. On the 
whole the tendency of the development of the two is towards a perfect harmony in 
which the knowledge of the universal interaction of natural forces would completely 



VI 

explain ;ill that takes place in iiuluslrial j)rocesses, and ou the other hand indusliial 
processes would be perfected by the application of a complete knowledge of the 
mechanism of nature. 

Thus, although there is a great dialinction between science and practice, each is to a 
large extent dependent on the aid of tlie other. Their influence upon each other 
could be illustrated by the history of any branch of science : it is illustrated by the 
history of biological arts and sciences. The discovery that the great depths of the 
ocean were inhabited by living animals was directly due to the laying of the telegraph 
cable from Europe to America. The medical sciences, anatomy and physiology, sprang 
not solely from the desire for knowledge, but from the practice of the healing art, 
and the desire to improve that art. Botany took its rise from the knowledge of 
simples, the use of plants as remedies for diseases and disorders of the human body. 
Zoology and comparative anatomy and physiology have been largely aided in their 
development by the medical sciences. Marine zoology has ever been to a great degree 
dependent on the assistance of fishermen and fishing engines. Science has received 
definite additions from investigations carried out with the object of cultivating oysters. 
The explanation of evolution is sought in the study of the variations of domesticated 
animals and plants. Are there, on the other hand, any cases in which human arts and 
industries have directly benefited by the biological sciences ? To answer this question 
by even briefly enumerating the recent discoveries concerning animal and vegetable 
parasites which have revolutionised the practice of agriculture would require a 
volume. But it must be confessed that the fishing industry has hitherto, in tliis 
country at least, not been greatly benefited by the scientific knowledge of fishes hitherto 
available. Yet zoological science and the methods of that science have not been 
entirely without efiect upon tlie supply of aquatic animals for the wants of man. 
Oyster-culture based upon scientific knowledge has been very successful in Holland 
and France. Knowledge of the conditions of life of the salmon has been apjjlied to 
maintain and increase the abundance of that fish in this country, and of allied fishes 
in America. The shad has been propagated with great success on tlie Atlantic coast 
of the United States. It remains true that there exists a great deal of scienlific 
knowledge of marine fishes which has hitherto not at all aflL'cted the sea-fishing 
industry. But it is also true that no great endeavours have yet been made to 
bring science and practice in this direction into relation with one another, and also 
tliat our knowledge of the life of marine fishes is in many respects still extremel}- 



Vll 

limited. The structure of tliese fishes and their place in the general classification of 
the animal kingdom has been to some extent ascertained, but of their conditions of life, 
their food, rate of growth, the causes which favour or limit their abundance, we still 
know very little. It was only in 1864, when Professor Sars identified the floating eggs 
of the cod, that it was first discovered that the eggs of any marine fish passed through 
their development while suspended in the surface waters of the sea. The know- 
ledge of structure and classification is not entirely useless from the practical point 
of view, for it is absolutely necessary as a basis from which to investigate the difl'erent 
conditions of life of the different species. The species must be considered separately, 
for their mutual relations are so complicated that it is impossible to deal witli them 
together. 

The object of the present work is to place side by side the results of a scientific 
study of the common sole and an account of the present condition of the sole fishery, 
and then to consider what are the possible practical applications of the former to the 
purpose of maintaining or increasing the supply of soles available for the market. 

The work was undertaken under instructions from the Council of tlie Marine 
Biological Association, and the investigations described were carried out at the 
Association's Laboratory at Plymouth. Nearly the whole of my time and energy since 
November, 1888, have been devoted to the subject. The instructions of the Council 
were quite general, but from Professor Lankester I have received much guidance 
as to the scope of the investigations and the plan of the book. The responsibility, 
however, for all the views and statements rests entirely upon myself. When studying 
the taxonomical part of the subject in November, 1889, I visited the British Museum 
of Natural History, and examined all the type specimens of European species of sole. 
I have to thank Dr. Giinther for the courtesy and assistance I then received from 
him. At that time I gathered from conversations with him that he still believed 
in an English species, Solea aurantiaca, distinct from the Solea lascaris of either Risso 
or Bonaparte. I was therefore surprised to see tliat in a communication to the 
Zoological Society in January last lie abandoned this opinion, and adopted the 
conclusion of most recent writers on the subject — that the English and the Mediter- 
ranean form belong to the same species. My discussion of the question in the 
present work was written in November, 1889, immediately after my visit to the 
national collection. 

I have nnich pleasiiro in thanking Mr. Dunn, of Mevagissey, and my iViend Eupert 



vni 



"Vallentin, Esq., of Falmouth, for the most important assistance they rendered me in 
procuring specimens of tlie sole in the younger stages of growth. I am still more 
deeply indebted to Miss Annie Willis for the skill and care \vluch she devoted to the 
water-colour drawings reproduced in Plates I to IX. The beauty, minuteness of detail, 
and artistic finish of her work are evident enough in the lithographic copies, and I need 
only add that the drawings were executed from the actual objects under my direct 
supervision, and that I can answer for their perfect faithfulness. 

J. T. C. 



PLyMOUTH, 

March 13, 1890. 



Part I. 



TAXONOMICAL. 



CHAPTER I. 

CLASSIFICATION OF THE FLAT-FISHES. 

It is a matter of general knowledge and experience that the various kinds of flat- 
fishes resemble one another and differ from all other fishes in these conspicuous 
features : that their form is very flat, that one side is coloured and the other of a pure 
opaque white, and that there are two eyes on the coloured side and none on the white 
side. It is further generally known, from the observation of such fishes in the living 
state in aquaria, that when alive they are usually resting on the white side at the 
bottom of the water, sometimes gliding gently over the ground, sometimes burying 
themselves in the sand, which is the material on which they are accustomed to live, 
and only occasionally rising up from the bottom and swimming in a horizontal position 
through the water. The common sole is also as a rule recognised by everybody as a 
particular kind of flat-fish, being readily distinguished by its gently curved outline, 
especially by the regular, almost semicircular, shape of the snout, and by the dull 
brown colour of its upper side after death. 

But this is only true of the sole as it is usually seen by the majority of people, that 
is in its adult condition. Ordinary habits of observation are not sufficient to dis- 
tinguish the sole in its very young condition from other kinds of flat-fishes : only 
naturalists are able to separate the kinds from one another among individuals from 
one to three inches in length. Even fishermen, who might be supposed to have 
unusual opportunities of comparing different kinds of fishes, but who, as a matter of 
fact, have usually no leisure and no superfluous energy to devote to accurate and 
minute observation, constantly mistake various kinds of flat-fishes in their young stages 
for young soles. The reason of this is not that the young fishes between one and 
three inches long differ in their characters from full-grown specimens, but simply that 
the characteristic features are on a much smaller scale, and therefore are not seen 
without attentive observation. 

Untrained powers of observation are also unable to compare the degree of difference 
between one kind of flat-fish and another. The plaice and flounder are named 
independently ; but a fish which resembles the plaice and flounder far more closely 
than it does the sole is sold under the name of merry-sole in Devonsliire and lemon- 
sole in London. This may be partly due to an inclination to enhance its value in the 

B 2 



4 

eyes of the consumer. Again, more than one kind of sole is sometimes sold under 
that name. 

It is evident, then, that before we commence the study of the common sole we must 
make ourselves accurately acquainted with its special features, so that we may not 
mistake other kinds for it, and may identify it with certainty at all stages of its 
existence. In order to discover these special features we must compare all the kinds 
of flat-fishes with other fishes and with one another and thus ascertain — 1st, what 
features are common to all of them ; 2nd, what features are common to certain divi- 
sions of them and especially to the division which includes the sole ; 3rd, what are the 
differences between the several kinds or species included in this particular division. 

In order to study the characters of the flat-fishes we must of course give names to 
their various organs ; but all the bony fishes are made up of the same organs in 
different shapes and sizes and in various proportions to one another. Thus we have 
only to examine the sole and compare it with a fish of the more usual structure in 
order to recognise the various organs which have long borne appropriate names. 

In any fish of the ordinary type, for example, a salmon, lierring, cod, perch, 
mackerel, &c., the two sides resemble one another in form, structure, and colour, and 
correspond to one another in the position and direction of their component organs. 
In other words, all the organs, with the exception of some of the internal, are in pairs, 
the two members of each pair being situated on opposite sides of the middle plane of 
the body, at the same level, and at equal distances from it. This plan of structure 
occurs in the majority of fishes and nearly all the otlier vertebrates, and also in the 
greater number of the lower animals, for instance in Crustacea and insects. To 
obtain a distinct idea of it we may reflect that the body of any animal in which it 
occurs, say a normal fish, a dog, or a man, has length, thickness, and breadth. The 
length is measured from tlie head to the posterior end of the body, the thickness from 
the back to the ventral surface, tlie breadth from side to side. Now the organs at 
opposite ends of the line which measures length are utterly different in form and 
structure, and those at the back are equally diflerent from those opposite to them at 
the ventral surface. But, wherever we measure the breadth, the parts at one end of 
the line along which we measure will be exactly similar in form and structure to 
those at the other, but exactly reversed in horizontal direction, This structural 
feature is called bilateral symniistry. 

The greater number of fishes are bilaterally sj-mmetrical, and the line along the 
surface which separates the two similar halves passes between the eyes at an equal 
distance from each. If we look for the line which divides two similar halves in the 
sole we shall not be able to find it. It is obvious that a line drawn between the eyes 
does not divide the head into two equal and similar parts ; but if we look for the 
paired organs of the ordinary fish in tlie sole we shall find in most cases that one of 
each pair is on the coloured or upper side of the sole, and the other on the white or 
lower side, but that in many cases the two members of each pair are not so exactly 



similar as they are in the ordinary fish. Thus in the sole there is a gill-cover or 
operculum on the upper side and another on the lower, and beneath each is a similar 
gill-apparatus ; half tlie mouth is on the upper side and half on the lower ; there are 
two nostrils on the upper side and two on the lower ; a pectoral fin and a pelvic fin on 
the upper side and two corresponding fins on the lower ; scales on the upper side and 
similar scales with a corresponding arrangement on the lower ; and finally a line of 
peculiar scales, a lateral line, along the middle of the upper side and a similar line on 
the lower. It follows, therefore, that the long continuous fins along the two edges of 
the sole correspond to the median fins of the ordinary fish, and as we find the anus and 
the junction of the gill arches on one edge of the sole, this edge corresponds to the 
ventral median line of the ordinary fish, so that the elongated fringing fins of the 
sole are the dorsal and ventral median fins respectively ; the ventral median fin is 
generally called the anal fin. We thus find that the upper side of the sole is the right 
side and the lower the left, and the edge on which the anus opens is the ventral edge, 
the other the dorsal. But the two eyes, though in other respects similar to the two 
eyes of an ordinarj" fish, are both on the right side, one nearer to the dorsal edge, the 
other nearer to the ventral. We may distinguish these eyes as the dorsal and ventral 
respectively, and even without further knowledge we might consider it probable that 
the dorsal eye corresponds to the left eye of an ordinary fish and the ventral to the 
right, and the idea would naturally occur to us that the left eye in the sole had been 
somehow drawn out of its original position on the left side and carried round to the 
right side. 

The fins of the sole are all supported by flexible or soft rays ; none of the rays are 
rigid pointed spines ; but this is a character which occurs in certain symmetrical 
fishes, for example, the cod and whiting. The possession of a single elongated 
median dorsal fin and a single similar ventral fin is also not peculiar to the sole : some 
members of the cod family have but a single dorsal and ventral fin. But no 
symmetrical fish has a dorsal fin extending so far forwards as the sole : in the latter 
this fill is continued to a point on the edge of the body anterior to the eyes, and in 
every flat-fish, except one species, it extends at least as far as a point above the dorsal 
eye, while in all symmetrical fishes the limit is somewhat behind the eyes. 

The lower or left side of the sole differs from the right side not only in being white 
instead of coloured, but also in being flatter, and the fin-rays of the meiilian fins are 
also more prominent on this side. 

The examination of other flat fishes will show that they resemble the sole and difler 
from symmetrical fishes in the features just mentioned, if we except the fact that in 
some kinds it is the left side and not the right which is coloured and which bears the 
eyes. Thus the turbot and brill have the eyes on the left side, while the plaice 
flounder, dab, and halibut, like the sole, have them on the right side. 

All the various kinds of flat fishes thus resemble one another and difler from 
symmetrical fishes in the particulars now described, which may be thus summarised : — 



Body much compressed bilaterally and extended dorso-ventrally : one side, on ■wliicli 
the fish rests during life, opaque white, flatter than the other, which is more convex 
and exhibits colour and markings : both ej^es on the coloured side of the head. 
Pectoral and pelivc fins small, the former sometimes absent ; a single elongated dorsal 
fin which extends forwards as far as or beyond the level of the dorsal eye, except in 
one instance where it ends a little behind the eye ; a single elongated anal fin 
extending fi-om the base of the tail to the anus, which is a short distance behind the 
opercular apertures. 

The fishes thus characterised form a single family — the Pleuronectidce ( = side- 
swimmers, from Greek TrXevpd, the side ; vyjx^^^ I swim). The large number of kinds 
or species which can be distinguished among them are divided into a number of groups 
according to the degree of difierence between them, any two species of the same group 
being much more closely similar to one another than to the members of any other 
group. These groups are the genera. Thus the diflerence between a plaice and a 
sole is much greater than the diflerence between a plaice and a flounder. The plaice 
and the flounder resemble each other in the shape of the body, in the large prominent 
eyes, and the small terminal mouth and pointed snout. Again, if we compare a turbot 
and a brill we find that they resemble one another very closely : they both have a deep 
straight mouth cleft, the anterior end of which is at the extreme aj)ex of the snout, and 
both have a more or less rhomboidal shape. 

The various kinds of sole are all distinguished from other flat fishes by the gradual 
and regular curve formed by the outline of the body, which, excepting the tail, is 
almost a perfect oval, the semicircular form of the snout being specially characteristic. 
'J'he dorsal fin connnences on the snout, and is not continuous with the caudal fin ; the 
cleft of the mouth on each side is curved downwards. The mouth is asymmetrical, the 
jaws being stronger on the lower side, and only on this side containing teeth, which 
are small and slender. The eyes are on the right side and small, the dorsal being in 
advance of the ventral. The scales are small and fringed with small projecting spines, 
that is, are of tbe kind called ctenoid. Tlie lateral line is straight from the head to the 
tail, and runs along the middle of each side, but it also sends a curved branch forwards 
on the head which runs parallel to the base of the dorsal fin towards the snout. 

All the Pleuronectidce exliibiting the above features are called Solea, with a 
distinguishing adjective to indicate the particular kind or species referred to. In 
otlier words, the species which resemble one another in these particulars and differ 
only in more minute details are classed together in a genus which bears the Latin 
name Solea in the universal language of Zoology. 

There are other kinds of sole besides the common sole, that is to say, there are other 
kinds of flat-fishes which resemble the sole in all the features in which the sole difters 
from the turbot or the flounder, but difier from it in more minute details. One kind 
is sometimes sold tofjether with the common sole without bein" distinguished, and 
sometimes is distinguished as the sand sole. It diflers from the common sole chiefly 



in two characters : (1) it is somewhat lighter in colour after death, and instead of large 
black blotches on the coloured side it has small black specks scattered almost 
uniformly over the surface ; (2) the anterior nostril of the lower side is very large and 
conspicuous, it is dilated and has folds radiating from its wall into its cavity. At 
Plymouth and other places on the south coast of Devon and Cornwall another flat- 
fish is commonly sold which is called the thick-back. This is evidently a kind of sole, 
but is distinguished by its smaller size, and by its colour and marking, which consists 
of black transverse stripes on a red ground. 

Several kinds of flat-fishes are obtained from British seas, which are too small and 
too scarce to be of any value as food, but which of course have been studied by 
zoologists equally with the edible species. 

After studying all the species of flat-fishes brought together in the British Museum 
from all parts of the world, Dr. GUnther has classified them in thirty-four genera, 
including Solea. But of these only seven include species which occur on the British 
coasts. Zoologists often differ as to the limitations of genera, because it is in many 
cases difficult to decide whether several species differ from one another to an equal 
degree and ought therefore to be classed in a single genus, or whether they differ in 
different degrees and ought to be separated into two or more genera. Eecent 
authorities also recognise seven genera among British forms — namely, Hippoglossus, 
Hippoglossoides, Rhombus, Zeugopterus, Arnoglossus, Pleuronecies, and Solea. The 
external differences which distinguish the genera and species of British forms maj^ be 
presented analytically thus : — 

A. Eyes on the left side ; mouth terminal ; teeth on both sides ; ventral eye anterior 
to the dorsal. 

1 . Rhoinhus. Shape rhomboidal, middle of the body being very broad ; 

mouth large ; lateral line with a semicircular curve anteriorly. 

Rhombus maximiis, the Turbot. No ordinary scales, but pointed 
tubercles uniformly scattered over skin. 

Rhombus la'vis, the Brill. Small scales ; no tubercles. 

2. Zeugopterus. Shape almost rectangular, anterior end obtuse ; lateral line 

with a semicircular curve anteriorly ; scales ctenoid. 

Zeugopterus unimaculatus, first dorsal ray elongated and undivided, 
median fins not prolonged under the base of the tail ; a conspicuous 
large dark spot towards the posterior end of the lateral line. 

Zeugopterus punctatus, first dorsal ray not elongated, median fins 
prolonged under the base of the tail. 

3. Arnoglossus. Shape oval, rather narrow, with sharp snout; eyes large, 

almost level, ventral slightly more advanced. Cleft of mouth deep. 
Teeth small, one or two rows in bolh jaws ; present or absent from the 
vomer ; none on the palatines. Gill- membranes somewhat broadl}' united 



8 

at the throat. Dorsal Gn commencing on the snout in front of the ej'cs, 
and not continuous with caudal. Nearly all the rays of the dorsal and 
anal simple and undivided. Scales somewhat large, easil}'- detached, 
ctenoid. Lateral line with a rectangular bight above the pectoral. 

Arnoglos-nis meijastoi/ia (Megrim at Plymouth). Teeth on the vomer. 
Anterior dorsal rays united by membrane for half of their length. The 
base of the dorsal fin not passing on to the lower side of the head 
anteriorly. Anterior nostril of the lower side protected by a broad flap 
of flexible membrane. Eyes very large. Scales not so deciduous as in 
the following species. Snout pointed. 

Arnofjlossus laterna (Scald-fish or Scald-back at Plymouth). No teeth 
on the vomer. Anterior dorsal rays free and separate ; the membrane 
of the rest of the fin very slight, the rays easily becoming separate. 
The anterior rays of the dorsal fin arise from the lower surface of 
the head. Eyes not very large. Snout somewhat blunt. The base of 
the left pelvic fin extends from the throat to the anus, and behind it 
are one or two prominent spines. The four anterior rays of the dorsal 
fin are very thick and much elongated in the male, not in the female. 
Arnoglosstis lophotes, GUnther, is the male. 

JJ. Eyes on the right side. 

I. Mouth terminal and large, teeth on both sides. 

1. Ilippoglossus. Shape lanceolate ; dorsal fin commencing above the dorsal 

eye ; scales cycloid. Lateral line with a slight curve anteriorly. 
Hippoglossus vulgaris, the Halibut. 

2. Ilippoglossoides. Anterior end not much narrowed; dorsal and ventral 

ed<xes rather straight : scales ctenoid. Lateral line straight. 
Hippoglossoides limandoides, the Long Hough Dab. 

IL Mouth terminal and extremely small ; teeth most developed on the lower 
side. 

L Pleuroiiectes. Dorsal fin commencing above the dorsal eye ; eyes large 
and prominent ; scales small or rudimentary. 

Pleuronectes platessa, the Plaice. Bony tubercles on the interorbital 
ridge. Bright red spots ; scales uniform. Lateral line nearly straight. 

Pleuronectes microcephalus, the Merry-sole or Lemon-sole. Skin slimy. 
Lateral line with a very small anterior curve. Colours mottled with a 
good deal of yellow ; scales cycloid. Shape somewhat rectangular. 

Pleuronectes cynoglossus, the Pole-flounder or Witch. Shape elongated; 
dorsal and ventral edges very gradually curved. Lateral line straight. 



Pleuronectes fiesus, tlie Common Flounder. Ossicles at base of dorsal 
and anal fins. Scales rough along lateral line, elsewhere rudimentary. 

Pleuronectes limanda. Shape rhomboidal; snout pointed. Lateral 
line with a small semicircular curve anteriorly. 

III. Mouth rather small, and not terminal, but curved down to the ventral 
edge ; teeth present only on the lower side. 

1. Solea. The shape oval, outline of tlie snout regularly semicircular. Scales 
ctenoid. Lateral line straight, l)ut with an anterior dorsal curve on 
the head. Tactile filaments on the lower side of tlie snout. Paired 
fin^ may be rudimentary or absent. The dorsal eye anterior to tlie 
lower. 

Solea vulgaris, the Common Sole. Pectorals on both sides of con- 
siderable size ; nostrils on the two sides similar ; filaments of the under 
side of the snout closely crowded together not forming any pattern. 
Markings of the upper side consisting of longitudinal series of black 
blotches on a j-ellowisli-brown ground. 

Solea lascaris, the French 'Sole or Sand Sole. Differs from tlie 
preceding in two characters — viz., the anterior nostril on the lower side 
is dilated and fringed internally ; each of the black blotches of the 
preceding species is represented by a number of small black specks. 

Solea varicgata, the Thick-back. Nostrils on both sides similar ; 
pectcral and pelvic fins rudimentary ; filaments of the lower side of the 
snout connected at their bases by membranes which surround square 
depressions. Mouth more terminal and less curved than in tlie other 
species. Markings consist of five transverse dark bands. 

Solea lutea. Eesembles the preceding in other respects, but has the 
mouth much curved, the dorsal fin commencing on tlie extreme 
anterior end of the snout. The markings consist of dark blotches 
arranged as in S. vulgaris, but there is in addition a thin black line 
along every fifth or sixth ray in the dorsal and anal fins. 

Solea Greenii, a new species just defined by Dr. Glinther, has tlie 
scales, fin rays, and filaments of the left side of the head as in vulgaris, 
but rudimentary pectorals. 

Plates I to VII, which exhiljil with great accuracy the natural appearance of the 
fish, will illustrate the distinguishing external features of the four commoner British 
species of sole. But although the above-mentioned characters are those which 
principally distinguish the species from one another, they do not exactly resemble one 
another in every other respect. We may jiroceed to study their characters in greater 

c 



10 

detail, in order to obtain a complete knowledge of their specific peculiarities. In 
describing the characters of a fish, it is usual to commence by counting tho fin-rays in 
each fin, the number of scales in the lateral line, wherever this is possible, the number 
of vertebnc, and the number of rays whicli support the membrane covering the gills 
beneath the operculum ; these are called the branchiostegal rays. These numbers 
are all put down in succession with initial lettei's to indicate the organs they refer to, 
so as to form a numerical foi'mula. Thus : — 



B. := Branchiostegal. 
D. = Dorsal fin. 
A. = Anal fin. 
L.l. = Lateral line. 



Pt. = Pectoral fin. 
Pv. = Pelvic fin. 
C. = Caudal fin. 
Vert. = Vertebras. 



The proportions of the fish are expressed numerically by stating the number of 
times a given length is contained in the total length : the reason of this is that the 
measurements are made with a pair of compasses, which are first adjusted to the length 
of a certain organ, and then used to mark olT successive lengths equal to this along the 
body-length. 



11 



CHAPTER II. 

HISTOEY OF THE GENUS SOLEA. 

The flat-fislies liave been always placed together iu one group in all attempts to classify 
fishes from the time of the ancient Greeks and Eomans up to the present. Thus 
Aristotle called them »/;rjTT&jSei9. But in ancient times other fishes of a flat sl^ape, 
but symmetrical, like tlie dorey and the skate, have often Ijeen united with them. Thus 
Eondelet includes among the " poissons plats" the dorey and two other symmetrical, 
fishes and all the skates and rays. In the ancient and pre-Linntean times ideas 
of classification were somewhat vague ; the idea of genus and species existed, thouo-h 
it was not accurately defined, but degrees of classification regularly subordinated to 
one another could not be established by men who had little real knowledo-e of the 
structure and physiology of animals. Eoudelet includes all marine animals among his 
" Poissons," yet his arrangement of the true Pleuronectidas in genera and species is 
more similar to that which is now accepted than the cltissification adopted by Artedi 
and Linnasus. Eondelet describes the genus Rhombus with two species, one with 
spines and the other without, the turbot and the brill ; the genus Ehomhoides ; 
Citltarus with two species ; Passer with four species. Passer, the plaice. Passer qiiad- 
ratuhis, Passer liraanda, and Passer fiesus (the flounder) ; the genus Solea, with six 
species, Solea, the common sole, Solea oculata {la Petjouse), la Pole, Armoglossus, Solea 
lingtda, and Hippoglossus. 

Artedi arranged all the flat fishes into one genus — Pleuronectes, a name which he 
introduced into zoology for the first time, and LinnsEus followed liis example. The 
l'2th edition of the " Sj^stema Naturae" was published in 1766. Tlie successors of 
Linnseus for some time continued to follow him and Artedi, merely dividiiig the genus 
iu an arbitrary way into subgenera. Lacepede, in his '• Histoire Nat. des Poissons," 
published in 1798, defines four subgenera of Pleiironectes, but without o-ivino- them 
distinguishing names : the first of them comprises only the halibut and the flounder, 
united because their eyes are on the right side and they have a curve in tlie lateral 
line. Similarly, Eisso, in his " Ichthyologie de Nice," 1810, arranges the species under 
two subgenera, according to the side on which the eyes are situated. 

Quensel in 1806 divided the senus into two, Avith the following definitions: — 
Pleuronectes, having complete jaws not covered with scales ; the maxillary dilated 

c 2 



12 

and free at its extremity ; tlie mandible with cutaneous folds between its limbs at the 
chin. Gill-opening extending above the opercular angle or at least above the pectoral. 
The lower eye more anterior than the upper one, and the nostrils distant from the 
jaws, that of the blind side being near the dorsal edge. 

Solea, in which the jaws are covered with scales, the superior one not fully 
developed, and the scaly mandible not showing the usual folds at the chin. Gill- 
openings wholly below the pectorals. The inferior eye farther back than the superior 
one. Nostrils on both sides near the jaws. All the fui-rays divided, no spine in the 
anal. (Richardson's Yarrell, Vol I., p. 608.) 

In the " Rcgne Animal," first edition, 1817, Cuvier makes the Iinua?an genus into 
a family, which he calls simply " poissons plats," and divides it into genera and species 
as follows : — 

Platessa, including the plaice, Platessa platessa ; the flounder, Platessa Jlesus ; the 
dab, Platessa limanda. 

Ilippoijlossus. including the PI. hippoglossus of Linnaeus, and several species of the 
Mediterranean described by other authors. 

Rhombus, including Rhombus maximus, the turbot and the brill, the PI. nwlus of 
llisso (apparently an Arnaglossus), and other species in which the upper eye 
is at a great distance above and behind the lower. 

Solea, including tlie common sole, PI. solea, Lin., the Pole of Belon, the S 'lea 
oculata of Hondelet, the Peyou.se of Eisso, and the lascaris and theophihis of 
the same author. Also certain foreign species in which the vertical fins are 
continuous, PL zebra, Bloch, PI. plagusia, Lin. (These species now form the 
genus Plagusia.) 

The Monochires, in which the right pectoral is very small, and the left minute 
or altogether wanting, e.<i., Linguatula, Eondelet, and the Achires, which have 
no pectorals at all, are mentioned apparently as subgenera. Those Achires in 
which the vertical fins are continuous with the caudal are distinguished as 
Pl'igK.'^ia. 

The definition of Solea given by Cuvier is as follows : — 

" Their peculiar character is that the month is twisted and as it were monstrous on 
the side opposite to the eyes, and furnished on that side only with slender teeth closely 
crowded together like the pile of velvet, while the side where the eyes are has no teeth. 
Their ft)rm is oblong, their snout round and always projecting beyond the mouth; the 
dorsal fin conunencing over the mouth, and extending like the anal up to the caudal. 
Their lateral line is straight ; the side of the head opposite to the eyes is generally 
furnished with a sort of villosity. Their intestine is long, with several convolutions, 
and without creca." 

It is evident that this definition of the genus admits of but liitle improvement. 
Cuvier obviously meant the Monochires, Achires, and Plajusia to l)e mere subgenera 



13 

indicating the grouping of the various species. But subsequent authors iVequently 
raised these divisions to the rank of distinct genera. Bonaparte, 1841, separated the 
last subdivision of Cuvier only as a distinct genus, namely, Plagusia. 

Dr. Glinther, in his important work, " The British Museum Catalogue of Fishes," 
gives a comprehensive classification of the Pleuronectida3, which includes all the 
forms up to that time described in the literature or represented in the great national 
collection. He distinguishes in all thirty-four genera, many of which are entirely 
new, while the limits and definitions of tlie rest are revised. His definition of Solea 
is as follows : — 

Eyes on the right side, the upper being more or less in advance of the lower. Cleft 
of the mouth narrow, twisted round to the left side. Teeth on the blind side only, 
where they are villiform, forming bands ; no vomerine or palatine teeth. The dorsal 
tin commences on the snout, and is not confluent with the caudal, Scales very small ; 
ctenoid. Lateral line straight. 

Thus the chief difference between this definition and Cuvier's is that it excludes all 
the forms in which the longitudinal fins are continuous with the caudal. All the British 
forms of sole described in the present work are included l^y Glinther in the genus Solea. 
But almost every author defines the genera of Pleuronectid^e, even at the present day, 
in some degree after his own fashion. There is a general agreement, together with 
differences of opinion on certain points. In tlie Pleuronectidte, as in nearly all families 
of animals, there are certain well-marked species which are recognised by all naturalists. 
There are others, especially those founded upon a small number of specimens, which 
are more difficult to separate, and concerning whicli differences of opinion exist. But 
the question of the arrangement of the species into genera gives rise to much greater 
differences of opinion. The arrangement of course depends on which of the characters 
possessed by several species in common, are taken as characterising a genus. If one 
character is taken, a certain number of species are united by it ; if another is taken 
tlie same species are scattered among other genera. Thus the fish called in this work 
Arnoglossus megastoina is variously placed. By Giinther it is placed in the genus 
Rhombus, because it possesses teeth on the vomer. By Moreau, whose arrangement 
seems to me more original than natural, it is placed in the genus PJeuronedes. The 
characters in which the species agrees with Arnoglossus Interna seem to me to be more 
numerous and important than the pi'esence or absence of vomerine teeth, and I liave 
therefore followed those authors who include it in the genus Arnoglossus. 

In describing tlie British species I shall give not merely the range of variation 
of each numerical character, but the actual numbers observed in several individuals. 
It must be pointed out that the number of scales in the lateral line is always 
obtained not by counting the scales in the line itself, but the series of oblique trans- 
verse rows of scales which cross the lateral line ; the scales are so arranged as to 
form rows which run obliquely downwards somewhat from before backwards, other 
rows which i-un more obliquely downwards and from behind forwards, and others, 



vbich are not 8o distinct, wliicli run straight from before backwards; it is the rows of 
the first kind which are counted. The number of these rows indicated by the letters 
L.l. is not so absohitely certain as the number of fin-raj's in a fin, for the rows of scales 
are counted from the commencement of the lateral line to the base of the tail, and as 
the lateral line is actually continued to the very extremity of the tail, while the scales 
diminish in size gradually at the base of the tail until they get so small that the rows 
cannot be counted, there is, of course, no definite point where the counting ceases. 



15 



CHArTER III. 



SOLEA VULGARIS, Quensel. 



[Plates I to V.] 



Synonymy. 

Pui^lXwaaov, Athen. vii, p. 288. 

" Lingnlaca," Varro and Plautus. 

" Solea," Ovid, V. 124 ; Plin., ix, c. 16. 

" Buglossus sive Solea," Rondeletius, xi, c. 11, p. 320, and other m'^diapval authors. 

" La Sole," Rondelet, 1558, French edition, Lyons, p. 256. 

" Plenronectes, sp.," Ai-tedi, 1734, Genera, p. 18, No. 6 ; Species, p. GO, No. 5 ; Synonymtn, 

p. 82, No. 8. 
" Plenronectes solea," Lin., Syst. Nat., 1, p. -157 ; Bloch, 1784, Fl^che Ben.tsr.hl., ii, p. 42, 

taf. 45; Lacepede, iv, p. 023; Donovan, 1808, Brit. Fish., in, pi. 52; Risso, 1810, 

Iclitli. Nice, p. 307. 
" Sole," Pennant, Brit. Zool, iii, p. 203. 
"La Sole," Duhamel, iii, sec. 9, p. 257, pi. 1. 
"Solea vulgaris," Quensel, 1806, Vet. Akad. Handl., p. 230; Risso, 1826, Nat. 

Hist. Eur. Mcr., iii, p. 247 ; Bonaparte, Fau7ia Ital., iii, 26 ; Giinther, 1862, 

Brit. Mils. Catal., iv, p. 463; Morean, 1881, Poissons de la France, p. 304; 

Francis Day, 1884, Fish. Gt. Brit, and Ire., p. 39, pi. cvi. 



Males. 


Females. 


Total length | 


16-9 cm. 
= 6f in. 


264 cm. 
= 10| in. 


33-2 cm. 
= 13TVin. 


17-6 cm. 
= 6ffin. 


19-4 cm. 


35'6 cm. 
= 14 in. 


38 cm. 
= 15 in. 


Length 1^ 
height / 


3f 


3tV 


H 


H 


3 


3i 


3ft 


Length ] 
head / 


H 


5| 


^ 


5f 


H 


6tV 


6 


D 


90 


83 


86 


86 


83 


81 


87 


A 


74 


69 


74 


69 


66 


73 


70 


C 


21 


20 


21 


20 


21 


22 


20 


Pt 


7 


8 


8 


8 


8 


7 r. 8 1. 


9 


Pv 


5 


5 


5 


5 


5 


5 


5 


L.l 


159 


155 


160 


153 


149 


166 


166 


Vert 


~~* 


50 


48 


— 


— 


50 


48 



A COMPARISON of the above figures gives the following results. There are no 
constant sexual differences in any of the ten characters given in the table, except 



16 

that the females reach the larger size, nor anj- constant differences depending on size, 
although it is possible that a slight increase in the number of rows of scales takes 
place in individuals which grow very large. The largest individuals in the above 
table have the largest number of rows of scales. The number of pelvic fin-rays is 
constant, that of the pectoral rays, and of the caudal, nearly so. The number of 
vertebrae varies very slightly. The range of the numbers of tlie dorsal and anal 
fin-rays is considerable, in the above specimens 83 to 90, and 66 to 74, respectively 
The range for the lateral line scales is greater, namely, 149 to 166. In all these cases 
examination of a greater number of specimens would duuljtless have extended the 
range. 

Fins. — The dorsal fin conuuences a little in front of the dorsal eye, but behind the 
apex of the snout. The right pectoral is scarcely longer than the left and is contained 
two and a half times in the length of the head. 

Exjes. — Longitudinal diameter of e\-e one-.sixth the length of the head ; scaled skin 
between the eyes equal in breadth to the longitudinal diameter of the eye ; distance of 
dorsal eye from edge of the snout equal to the longitudinal diameter of the eye. 
Posterior edge of dorsal eye on a level with the middle of the venti-al. 

Nostrils. — On the right side both nostrils are close together inmiediately in front 
of the ventral eye and close to the edge of the upper lip. Botli are tubulai-, the 
posterior a little the wider, the anterior the longer. On the left side the two nostrils 
are also thin walled tubes, the anterior being prominent and larger, the posterior quite 
obscure; the latter is about half an inch (in adult) above and behind the former. 

Mouth. — Extends backwards to beneath the middle of the ventral e3'e : the teeth 
on the lower side are slender rods set close together in a broad curved patch in each 
jaw. The villi on the under side of the snout are really connected at the base by 
slight membranes which enclose depressions of the surface, l)Ut the latter are very 
small and the villi are therefore closely crowded together. 

Scales.— On the right side extend over the whole surface of the head up to its very 
ed^es, on the lower side thev decrease in size in the neighbourhood of the villi and 
disappear where these are full\- developed. The villous area is bounded posteriorly 
by a straight transverse line running a short distance behind the angle of the mouth. 
One of the largest scales from the middle region of the right side of the body (PI. XIV, 1 ) 
has sixteen radiating rows of spines, five spines in each of the middle rows. 

The curved anterior portion of the lateral line is very distinct on the right side, 
and can be traced running parallel to the edge of the body right to the apex of the 
snout. On the lower side a similar curve exists, and in addition a line belonging to 
the same system which runs straight forwards from the origin of the former above the 
mouth, gi\'ing off transverse branches. 

Colour. — The dead sole in the market generally appears to be of a uniform dull 
dark brown on the upper side, but closer examination shows that there are black 
blotches as well on the brown ground. During life the colours are much brighter. 



17 

and the markings much more conspicuous. Altliough the colours vary with the 
ground on which the animal rests, this variation is only in depth of tint ; the 
markings are constant for the same individual, and vary but little in different 
individuals, they have therefore quite as much importance as a specific character as 
any other feature in the animal. 

The markings, then, in the living fish consist of large dark blotches and small white 
spots on a yellowish-grey ground. The dark blotches, brown or black according 
to their intensity, are ai-ranged sjonmetrically so as to form a definite pattern : the 
largest blotches are in three rows, one along the lateral line, one near the base of 
the dorsal, and one near that of the anal fin. Usually there are five or six of these 
blotches in each row, but in some specimens there may be as many as eight in one or 
more of the rows. The first blotch of the dorsal row is close behind the anterior 
curve of the lateral line, and the last near the base of the tail ; the first of the central 
row is just above the end of the pectoral fin, and the first of the ventral series is at 
the base of the pelvic fin. The first and last in each series are alwaj's fainter and 
smaller, while those in the centre of the series are larger and more conspicuous. In 
each of the intervals between the blotches in each series is a lighter white spot, 
smaller and with a more definite outline than the dark blotches. Other white spots 
frequently appear around the dark blotches. Between the central row of blotches, 
and each of the external rows is another row of similar blotches of smaller size ; 
these are closer together, nine or ten of them can be usually counted in each series, 
and in the intervals between them there are small white spots. These are the 
principal markings, but there are in additioji narrow irregular branching streaks of a 
lighter brown extending from the edges of the dark blotches over the spaces between 
them ; these streaks usually contain dark or black specks, but under certain conditions 
they are everywhere almost as dark as the blotches, and then the latter are connected 
together by an irregular network of black streaks. Outside the external series of 
blotches, between them and the bases of the dorsal and anal fins respectively, is a 
band free from markings where the ground colour is uniform and lighter than 
elsewhere. The dorsal and anal fins themselves exhibit three distinct longitudinal 
bands of colour ; the basal third is dark, being densely sprinkled with minute black 
specks on a yellow ground, the middle portion is yellow without the black specks, 
while the extreme edge is colourless, the membrane between the rays being here 
transparent, while the skin over the extremities of the rays themselves is opaque white. 
The extreme dorsal and ventral edge of the tail fin are opaque white, the external 
portion of the tail, including the terminal half, is yellow, this portion being continuous 
with the light band vdiicli lies within the bases of the dorsal and anal fins ; the 
internal and basal part of the tail is sprinkled with black like the l)asal jiart of the 
dorsal and anal fins. The right side of the head is coloured like the parts of the 
body-surface between the blotches, that is, with blacks specks connected by faint 
brown lines on a yellowish ground. 

D 



18 

The pectoral fin has usually a black spot on its outer half, but very often this spot is 
only light brown, its intensity varying according to the action of light upon tli»? 
animal. 

When we examine still more minutely the elements of the coloration now described, 
we find that each of them is compound, made up of still smaller markings which 
have a definite relation to the scales. The scales are imbricated like the tiles ou a 
roof, and the exposed portion of each, which projects backwards, has the shape 
of the sector of a circle. Except in the white spots, where the whole sector is 
opaque white, the basal angle of the sector is lightest in colour, and the colour 
deepens in intensity to the extreme border which is darkest. Even in the lightest 
part of the ground colour the border of each scale is distinctly defined by its 
brownish colour, wliile in the darkest part of the blotches and black specks the curved 
edge and the posterior half of the scale is black, while the anterior angle is light 
brown or even yellow. 

The scales do not extend right up to the edge of the transparent cornea of the eyes, 
the skin bordering the cornea is smooth, and coloured green with brown specks, the 
iris is vcllowish-grey marked with radiating brown lines. The pupil is black at its 
edfres, but in the centre of it is a beautiful iridescent spot which dissection shows to 
belong not to the surface of the cornea, but to that of the crystalline lens. 

This species, being abundant on both the shores of the Mediterranean and the 
Atlantic coasts of Europe, has been generally known since the earliest historical times. 
It is mentioned by some of the ancient historical writers as ^SouyXwcrcros by the 
Greeks, and llnr/nlaca or solea by the Romans. The former two names are taken from 
its resemblance in shape to the tongue, the latter from its resemblance to the sole of 
a shoe. Similar names are still in use in the various European languages : the 
Germans call it zuncje, the tongue, and we call it the sole. In Italy it is called in 
some places limjiia or Unguattula, in others sogliola. The name tongue is also used 
sometimes for small soles at Billingsgate. 

After the revival of learning in the sixteenth century, when the study of sj-stematic 
natural history began to develop, the name Buglossus or Solea, borrowed from the 
ancients, was used for this fish by all naturalists up to the time of Artedi, that is up 
to the commencement of the eighteenth century. 

Artedi, who died in 1 734, placed all the flat fishes which had previously been 
usually grouped together by the mediaeval ichthyologists, in one genus, Plewonectes, 
a name first introduced by himself. 

Linnaeus, who edited Artedi's works, added little to the knowledge of fishes beyond 
applying binomial terms to the species defined by the latter. He named the sole 
Pleuronecies solea, in which he was followed by a number of his successors. 

But it was soon found necessary to make the flat fishes not a single genus, but a 
family, classifying the diverse foi-ms under various genera. This was in reality a 
return to the practice of the pre-Linnasan naturalists, the results of Artedi's accurate 



1 



J9 

distinctions and Linnaeus' system of nomenclature being retained. The name Soleu 
vulgaris was first used by Quensel, a Swedish zoologist, in 180(3, and it has been 
generally employed since that time. The species has since then always formed the 
type of the genus, the number of species included with it varying in the systems of 
classification adopted by different ichthyologists. 



D 2 



2U 



CHAPTER IV. 



SOLEA LASCARIS, Bonaparte 



[Plate YI.] 



Synony my. 

' Plenroncctes lascaris," Ri.sso, 1810, Ichthyologie de Nice, p. 311. 

' Solea lascai-is," Risso, 1826, Hist. Nat. de I'Eitr. Mer., t. iii, p. 249. 

'Solea nasuta," Nordm, iu Bemid. Vmj. Russ. Merid. Zool., iii, Poissom, Tab. .31. 

'Solea lascari.s," Bonaparte, 1841, Fauna Italica, t. iii, 27*, with 2 figures. 

' Solea pegusa," Yarrell, 1829, Zuol. Journal, vol. iv, p. 4^37, pi. IG. 

' Lemon Sole," Yarrell. 18:?6. Urif. Fishes, first edition, vol. ii, p. 2G0. 

'Solea aurantiaca," Giinther, 1802, Cat. Brit. Mus., vol. iv, p. 407. 

' Solea la.scaris," Moreau, 1881, Poissons de la France, t. iii, p. 307. 

' Solea lascaris," Francis Day, 1884, Fishes, Gt. Brit, and Ire., vol. ii, p. 42, pi. 107 



Total length | 


Male. 


Females. 


17-2 cm. 
(ji* in. 


18-9 cm. 
7tV in. 


19-2 cm. 
7-i in. 


26-1 cm. 
IOtV in. 


Length \ 
height / 


2f 


2U 


. n 


m 


Leneth 1 
head J ' ' 










5; ' 


55 


H 


H 


D 


79 


81 


89 


82 


A 


07 


67 


70 


70 


C 


20 


20 


20 


20 


Pt 


9 


9 


8 


9 


Pv 


5 


5 


5 


6 


L.l 


125 


125 


123 


119 


Vert 


— 




46 


46 



Of tills species I have only been able to make a detailed examination of the four 
specimens whose numerical peculiarities are given in the above table. 

Comparison of the above characters with those of Solea vuhjaris shows that the 
presoit species is much broader in proportion to its length than the former, that the 
proportion of the length of the head to the total length is abt)ut the same, that the 
vertebras are fewer in number, and the scales larger iu proportion to the length of 
the body. 



21 

Fins. — The doisal commeuces just a trifle farther forwards than in ,S. vuhjo.ris, the 
base of the first ray being in line with the longitudinal diameter of the upper eye. 
The two pectorals are equal in length, and the length is contained two and' a half 
times in the length of the head. 

Eyes. — Dorsal eye half of its longitudinal diameter in front of the ventral, and 
more than its long diameter from the end of the snout; therefore not so near the edge 
as in vulgaris. 

Nostrils. — Both nostrils on the right side close together immediately in front of 
the ventral eye, both tubular, but the anterior considerably the longer. On the 
left side the anterior nostril is very broad and dilated, its edges being reflected 
outwards. These edges are covered externally with the slender papillas of the under 
surface of the snout. Internally there are a number of folds projecting from the 
inner surface of the nostril radiallv towards its centre, the ventral of these folds beino- 
thicker than the rest: the posterior nostril is tubular, narrow, and flaccid, and situated 
a short distance behind the upper part of the rim of the anterior. 

Mouth and Teeth as in vulgaris. The villi of the under side of the snout are finer 
and even more closely crowded than in vulgaris ; they are especially long and 
numerous round the edge of the dilated nostril. The villous area does not extend so 
far backwards as in vulgaris. The scales cover the w^hole right side of the head, as in 
vulgaris, but on the lower side they extend farther forwards above the nostrils, though 
lines of villi are developed along the transverse branches of the cephalic portion of the 
lateral line system. One of the scales from the middle region of the right side of the 
body has seventeen radiating rows of spines, six spines in each of the middle rows. 
(PI. XIV, 4.) 

The curved portion of the lateral line on the head on the right side is almost as dis- 
tinct as in vulgaris ; on the lower side the arrangement is the same as in that species. 

Colour. — After death the colour is much lighter than that of vulgaris, being yellow- 
brown instead of dull brown ; hence the name lemon sole by which the species is some- 
times called. In life the ground colour. is a brownish- j-ellow, and the markings consist 
of numerous small black specks scattered pretty uniformly over the whole surface. 
Careful examination shows that among these black specks, groups can be recognised 
which correspond in position with the black blotches of the common sole. In these 
groups the specks are somewhat larger and closer together than elsewhere. Thus the 
markings of the present species could be derived from those of vulgaris by taking 
away so much of the black of the blotches in the latter as to leave only a group of 
distinct specks. Among the specks are scattei-ed other small spots of a light blue 
colour ; these correspond to the white spots of vulgaris, but I have never seen them 
white. What was said of the relation of the colour to the scales in vtilgaris applies 
here also ; many of the scales are bright yellow at their bases. The colour of the fins 
resembles that in vulgaris ; there is a black spot on the outer half of the pectoral. 
The eves are coloured as in vulgaris. 



22 

The British form of Solea, which is distinguif-hed from the others by the dilatation of 
the left nostril, was first observed by Yarrell, who described and figured it in the 
" Zoological Journal," \v\. IV, in 1829, under the name Solea pegusa. His description is 
so bad that it would be impossible to identify the species by its means with certainty, 
but his plate shows the distinguishing characters quite clearly. Yarrell considered 
his specimens to belong to the species Plearonectes pegusa of Lacepede's " llistoire 
Naturelle des Poissons," Vol IV, 1803, and with the Pleuronectes pegusa of Eisso's 
" Ichthyologie de Nice," 1810, wliicli is called Monochirus f>egusa in the same author's 
" Hist. Nat. de I'Europe Meridionale." In the third edition of Yarrell's " British Fishes," 
Sir John Richardson identified this species as the Pleuronectes nasutus of Pallas' 
" Zoographia Rosso-Asiatica," 1811. 13ut the PL pegusa of Laccpede is the Solea 
ocellata of Giinther's Catalogue, the Pleuronectes ocellaius of Linnanis, the Solea 
ocidata of Eondelet, a well-marked species in which tlie nostril is not dilated ; and the 
Monochirus pegusa of Risso is another species of the Mediterranean which has no 
pectoral fin on the blind side, and in which also the left nostril is not dilated : it is the 
Solea monochir of Giinther's Catalogue. 

Yarrell's identification w^as therefore entirely incorrect, and Pallas' description of 
PL nasutus is so extremely vague that it is difiicult to ascertain to what species it 
referred. The specimens described by Pallas by the name n(t.sufus were taken in llic 
Theodosian Gulf in llic Black Sea. The Solea ocellata and Solea munochir both occur 
at Nice. 

Dr. Giinther, in his "Catalogue of the Fishes in the British Museum," Vol. IV, 18G2, 
distinguishes four species of Solea in which the left nostril is dilated and flattened. 
The British form, called by Yarrell Solea pegusa, the lemon sole, or French sole, is 
described as distinct from any other known species, and is named by Dr. Ciinther, 
Solea aurantiaca. The second of the four species is the Solea lascaris of Risso, the 
third Solea impar of Bennett, and the fourth Solea margaritifera of Giinther, another 
new species. I have examined m3-self the specimens in the collections of the British 
Museum, which Dr. Giinther thus described in his Catalogue, and in many respects I 
cannot agree with him in his arrangement and identification of them. 

Risso's original description of Solea lascaris is not very exact, and the small figure 
he gives is quite worthless ; it would be impossible to identify the species from the 
figure. The numbers of fin-rays he gives are as follows : — 

D. 85, A. G8, P. 7, V. .5, C. 15. 

He says that the colour is " fauve tigr(5 de noir, avec des reflets violets, parsem^s de 
points grisatres sur la surface droite." He says that the upper jaw covers the inferior 
in such a manner as to imitate the beak of a parroquet, and then continues: " Le 
dessous de la tete est orne de petits cils soyeux, blanchatres, entourant un long tube 
qui rc'^pand une humeur glaireuse." Now it is difiicult to understand how a naturalist 
could describe the dilated nostril of Yarrell's lemon sole as " un long tube," but as 



Risso makes no mention of any nostril on the nnder side of the head of any other 
species of Pleui'onectes, it is pretty evident that he was struck with a peculiar 
conspicuous nostril, such as exists in the English form we are considering. 

Bonaparte gives a good description and two excellent coloured figures in his " Fauna 
Italica," 1832-41, of a species which he calls Solea lascaris, and which he identifies 
with the Solea lascaris of Eisso's " Hist. Natur. de I'Europe Mer.," the Pleuronectes 
lascaris of the same author's " Ichthyologie de Nice." The fin formula given by 
Bonaparte is — 

D. 78, A. GO, P. 8,A^. 5, C. 19. 

It will be seen that the formula given hj Eisso agrees perfectly with the numbers 
observed by myself in British specimens, and that Bonaparte's differs so little from the 
lowest numbers found by me that, considering the rest of his description and his figures, 
there can be no doubt that the British specimens are of the same species as those 
observed by him. I conclude, therefore, that Bonaparte was correct in his identifi- 
cation, and that the British species of sole, described above, is the Solea lascaris of 
Eisso, more completely described by Bonaparte under the same name. 

Dr. GUnther identified the Solea irnpar of Bennett, of which he possessed only the 
original type specimen described by Bennett himself, with the Solea lascaris of 
Bonaparte. But, after carefully examining the specimen and the descriptions myself, 
I am unable to accept Dr. Giinther's conclusion. 

In the British Museum Catalogue a single specimen is identified as the Solea lascaris 
of Eisso. The chief peculiarities in Dr. Giinther's definition of this species are : the 
small size of the scales, the formula being LI. 150; the narrowness of the body, the 
height being one-third of the total length ; and the prolongation of the upper jaw, 
which is described as "produced into a longish lobe overhanging the lower." Of 
these characters only the last corresponds to anything in Eisso's description ; but I 
find that in my English specimens of the lemon sole, the upper jaw embraces the 
apex of the lower somewhat more than in the common sole, and that in the 
British Museum specimen the jaws do not differ to any appreciable extent in tliis 
respect from the English form. What Eisso says on this point applies to the English 
specimens. Eisso says nothing concerning the number of the scales nor of the 
proportion of breadth to length in his lascaris. 

The specimen which Giinther calls Solea lascaris came from Madeira ; the specimen 
called Solea impar by Bennett came from the Atlantic coast of North Africa. Eisso's 
Solea lascaris on the other hand, occurred at Nice, and Bonaparte's species is described 
as common at Venice, at Nice, and on the Eoman shores. In the collections under 
Dr. Giinther's charge there are specimens identified as Solea aitrantiaca from Lisbon 
and from Nice. Thus specimens of the same species as the English specimens have 
been found at Nice, while the l^ritish Museum possesses no specimen identified with 
Eisso's lascaris, or with Bonaparte's lascaris from any pari of the Mediterranean. 



24 

I will now shortly consider the question of the identification of the actua- specimens 
catalogued by Giinther. In the single specimen he calls lascaiis I could count only 
133 rows of scales, a number not much larger than the maximum 125 found by 
me in the English form. As for its narrowness, it had been forced into a bottle nmch 
loo narrow for it, and had in consequence been much compressed in breadth, so ihat 
I think it is scarcely possible to be certain about its proportions. I do not consider 
it toTse specifically distinct from the Solea lascaris of Bonaparte. 

Solea iiiipnr, Bennett, and Solea martjCiritifera, Giinther, must for tlie present be 
considered distinct. They differ from English specimens of Solea lascaris in numerical 
characters and also in colour. Both of them possess the marking characteristic of 
vulgaris, that is to say, there are dark spots arranged as in vulgaris, not divided up 
into small specks as in lascaris. Margaritifera is further distinguished by the con- 
spicuousness of the small white spots in the type specimen in spirit. It may be found 
in the future that Enghsli specimens of aS. lascaris exhibit a range of variation which 
would include both these species. 

Moreau, in his "Poissons de la France," 1881, also identifies the Solea aurantiaca of 
Giinther with the Solea lascaris of Eisso and Bonaparte, but he further includes the Solea 
impar, Bennett, in the same species, although it is not clear from his description 
whether he actually discovered by his own observation that the range of variation of 
lascaris included the characters of impar. Francis Day, in his "Fishes of Great Britain 
and Ireland," 1880-84, gives ihe same synonymy as Moreau. 



25 



CHAPTER V. 

SOLE A VARIEGATA, Fleming (Donovan). 
[Plate VII, Figs. 1 and 2.] 

Synonymy. 

" Pleuronectes variegatus," Donovan, 1808, Nat. Eisf. Brit. FisJies, pi. 117 
" Pleuronectes maugilli," Risso, 1810, Ichth. Nice, p. 310. 
" Rbombns mangili," Risso, 1826, Hist. Nat. Em: Mer., p. 255. 
" Variegated Sole," Yarrell, 1836, Brit. Fishes, first edition, p. 262. 
" Monochirus variegatus," Thompson, 1839, Ann. Nat. Sist., vol. ii, p. 404. 
" Solea mangilii," Bonaparte, 1841, Fauiia Italica, t. iii, 27**. 
" Solea variegata," Fleming, Brit. Animals, p. 197 ; Giintlier, Cafal, iv, p. 469. 
"Variegated Sole," Couch, Fish. Brit. Isles, iii, p. 203, pi. 177. 
" Solea variegata," Giinther, 1862, Bnt. Mus. Catal., vol. iv, p. 469. 
" Microchirus variegatus," Morean, 1821, Poissons de la France, t. iii, p. 317. 
" Solea variegata," Francis Day, 1884, Fishes Gt. Brit, and Ire., vol. ii, p. 43, pi. 105, 
fiff.l. 



Total len 



Length "1 
height J 
Length "I 



gth{ 



heai 
D. 
A. 
C. 
Pt. 
Pv. 
L.l. 
Vert. 


i 


i ■ ■ 



Males. 



17-2 cm. 
6f in. 

68 
63 
18 
4r. 11. 
5 
89 



17-9 cm. 
7 in. 

3| 

6^ 

74 

54 

18 

5 r. 1 1. 

5 
93 



18-3 cm. 



3i 



68 
62 
18 
4r. 21. 
5 
90 



191cm. 
7iin. 



6 

74 
58 
16 
4r. 11. 
6 
92 
40 



Females. 



19-7 cm. 


19-9 cm. 


20 cm. 


21 cm. 


7f in. 


m in. 


7|in. 


8iin. 


H 


H 


3^ 


3f 


6ii 


6| 


61 


61 


73 


69 


72 


72 


65 


65 


67 


56 


18 


18 


18 


18 


4r.21. 


4r. 11. 


4r. 11. 


6r. 31. 


5 


5 


6 


5 


88 


89 1 


89 


104 











41 



21 cm. 

81 in. 

71 

54 
. 18 
4r. 11. 
5 

87 

40 



The above figures show that while the two preceding species cannot be separated 
by the range of variation of the numbers of fin-rays in the dorsal and anal fins, the 



E 



2G 

present species can be so separated fioni those two. The range for the dorsal fin-rays 
in the above specimens is 68-74. Dr. Giintlier in his Catalogue gives 63-73, Day's 
"British Fishes" gives 65-74: the total ranrre recorded therefore is 63 to 74. Similarlv 
for the anal fin-rays the rang? in the above table is 52-58; GUnther gives 53-57; Day 
55-58, therefore the range in my table is the greatest recorded. Day gives the number 
of caudal fin-rays as 15, evidently not counting the smaller external rays. GUnther 
gives the scales of the lateral line as 85, Day as 85 to 90 ; the range in my specimens 
is 87-104. The number of vertebrge is here again very constant, and forms a good 
specific character, though it must be remembered that it is doubtful if it would serve 
to distinguish this species from all other known species of Solea. The proportion of 
breadth to length resembles that in vulgaris, and is therefore less than in lascaris, 
while the proportion of head to length is izsually less than in the other two species, but 
does not form a marked specific character. 

Fins. — The dorsal commences slightly farther forwards than in the two preceding 
species, the base of the first ray being actually nearer to the mouth than is the con- 
tinuation of the longitudinal diameter of the dorsal eye. The right i)ectoral is much 
larger than the left, but much smaller than the pectoral of the preceding species : its 
length is contained 3| to 4| times in the length of the head. The left pectoral is a 
mere insignificant filament, never more than ^ in. long, sometimes much smaller : it 
may contain one, two, or even three rudimentary fin-rays. 

Eyes. — The dorsal is only ^rd its own longitudinal diameter in front of the ventral, 
and f rds of the same lengtli from the edge of the snout. 

Xostrih.—T\ie two on the right side are in the same position as in the preceding 
species, but the posterior is smaller, and the anterior a more elongated tube than in 
tln'ni. Tlie two on the left side are situated as in «S. vulgaris, but are smaller and less 
conspicuous. 

Mouth, is much less curved downwards than in the two preceding species, the anterior 
end of the cleft being slightly more dorsal than the angle of the cleft, while in the two 
previous species it is considerably more ventral : the anterior end of the cleft is in fact 
on the same longitudinal level as the lower border of the ventral eye, while in the 
other two species it is considerably ventral to that level. The snout is more truncated 
than in the other two species, the apex scarcely projecting beyond tlie anterior end of 
the mouth-cleft. Two patches of rod-like teeth, as in the other species, cm the left side. 
The villi of the under side of the snout form short fringes at the edge of somewhat 
broad membranous folds of the skin, which have a reticulate arrangement enclosing 
quadrangular depressions of considerable size. This conspicuous reticulate arrange- 
inent of fringed membranes forms a distinct contrast to the closely crowded filaments 
in tlie two previous species (PI. VII, 2). 

The scales are absolutely broader than in any of the other British species, the 
breadth being almost equal to the length : they are- also much larger in proportion to 
the size of the body than in either of the two preceding species, as is evident from 



27 

tlie number of lateral line scales gis^en in the numerical table. A scale from the 
middle of the body (PI. XIV, 3) has 26 rows of spines, the middle rows having 8 spines 
each. 

The posterior vertical portion of the curve of the lateral line oii the right side of the 
head can be detected with difhculty, but the anterior part parallel to the base of the 
dorsal fin is wanting altogether. The branches of the lateral line system on the left 
side of the head in the previous species are also invisible in variegata. 

Colour. — The general colour is much brighter than that of either of the preceding 
species, being a distinctly reddish-brown with markings deepening to black. Of these 
markings the principal are five broad dark transverse bands, each of which terminates 
at either end in a large intensely black blotch situated partly on the side of the body, 
parti)' on the longitudinal fin. The first of these bands passes across just behind the 
pectoral fin, the others are at about equal distances, the last covering the ends of the 
dorsal and anal fins and the base of the tail. The central part of each band is only slightly 
darker than the neighbouring surface, but its anterior and posterior edges are usually 
very sharply defined. The darkening of the bands is produced by the presence of a thin 
black border at the edge of the scales, and the sudden extension of this black border 
over the whole scale produces the black blotch at each end of the band. Between the 
principal bands there are lighter areas which are again marked by one broad or two 
uarrow secondary bands : these also terminate in black patches, which in this case are 
usually situated on the outer part of the fin and extend to its edge : these patches are 
smaller and less regular than those belonging to the principal bands. There is a 
single secondary band not very well defined passing over the operculum : the rest of 
the head is almost uniform in colour. 

The anterior part of the tail, behind the last of the principal dark bands, is lighter 
than any other part of the body, its tint being yellow, while the rest of the tail is dark 
brown, the colour being here chiefly situated in the membrane between the rays. The 
tips of the dorsal and anal fin-rays are, as in the preceding species, opaque white. The 
Ijrightness of the red tint in the coloration fades considerably after death, approximating 
more to grey. 

What was said of the relation of the colour to the scales in the preceding species 
applies to this species also, but to a less degree; the extreme edge of every scale in the 
lighter parts is brown, but each scale is everywhere more uniform in colour than in 
vulgaris or lascavis. 

This species is well marked, and has generally been recognised by ichthyologists 
since its first discovery. It was first distinguished in England by Donovan, who 
obtained a single specimen from the London • market in 1807. He described and 
fitTured it in his "British Fishes" under the name Pleuronectes variegatus as a nondescript 
(new) species, although it has since been found that Duhamel had previously described 
it in his " Poissons de la France " under the name Pole panachee. Donovan's coloured 
figure is fairly good, but it represents the markings across the body as somewhat 

E 2 



28 

irregular interrupted stripes, instead of regular dark bands. It is possible that in 
Donovan's specimen the markings were as he figured them, but I have never seen such 
a variety of colouring, and it is more probable that in the single dead specimen from 
the market he did not perceive the markings accurately. 

The species was independently described as new by Eisso in his "Ichth. de Nice": that 
his species is the same is evident from his accurate description of the colour and 
markings and some other characters. He gave it the name Pleuronectes mangilli, after 
the surname of one of his contemporaries. In his later work, the " Hist. Nat. de I'Europe 
Moridionale," he calls the species Rhombus mangili. He gives no figure. 

Yarrell, in his first edition, gives a description and a woodcut from a specimen from 
Cornwall, but his figure looks as if it had been copied from Donovan's plate. YarreU 
incorrectly identified the species with the Solea lingida of Eondelet, the Linguatula of 
Cuvier, a mistake which he afterwards corrected in his supplement. 

Bonaparte gives an excellent description and a coloured figure of the species under 
the name Solea iiiangilii, identifying it with Eisso's species. His figure beautifully 
shows the dark transverse bands terminating at either end in black blotches which 
extend on to the fins. 

Gunther in his Catalogue gave a complete and correct account of the synonymy 
of the species ; his list of synonyms .shows that the species has been described 
independently at least four times, first as the Pole panachee by Duhamel, then as 
PL variegatus by Donovan, as PL microchirus by Delaroche, and as PL mangilli 
by Eisso. 

Moreau and Day give good descriptions of the species. The former gives no figure; 
the figure of the latter is not good, it gives the markings very incorrectly. 



29 



CHAPTER VI. 



SOLEA LUTEA, Bonapaute. 



[Plate VII, Figs. 3 and 4,] 



Synonymy. 

' Sulea parva sive lingula," Rondeletius, 1554, Be Fiscihus Marini!-, xi, c. 15, p. 31?, 

with fig. 
'La petite Sole," Rondelct, 1558, French edition. 
' Pleuronectes luteus," Risso, 1810, Ichth. de Nice, p. 312. 
'Rhombus lutens," Risso, 1826, Hist. Nat. Eur. Mer., t. iii, p. 257. 
' Solea lutea," Bonaparte, 1841, Fauna Italica, t. iii, p. 28. 

'Monochirus minutns," Parnell, 1837, Mag. Zool. and Bot., vol. i, p. 527, pi. 16, No. 2. 
' The Solenettc," Yarrell, 1839, Brit. Fishes, first edit. Suppl., p. 36. 
'Monochirus linguatulus," Thompson, 1839, Ann. Nat. Hist., vol. ii, p. 405. 
■ Solea lutea," Giinther, 1862, Cat. Brit. Mus., vol. iv, p. 469. 
' Solea miuuta," Giinther, 1862, ibid., p. 470. 



Total length . | 


Sex? 


Male. 


Female. 


5-2 cm. 


11'6 cm. 
4Ain. 


73 cm. 

2iin. 


Ill cm. 
41 in. 


Lengrth "[ 
height/ 


H 


H 


H 


3t^ 


Length ■] 
head J ' " ' 










4| 


H 


5 


5tV 


D 


73 


77 


73 


69 


A 


59 


63 


53 


55 


C 


16 


18 


16 


18 


Pt 


2r. 1 1. 


3 r. 11. 


4 r. 11. 


4 r. 11. 


Pv 


5 


5 


6 r. 3 1. 


5 


L.l 


— 


68 


62 


66 


Vert 


— 


— - 





37 



The above table includes the characters of only a very small number of specimens, as 
I have not had an ojjportunity of examining more. The measurements of the total 
length show that this is the smallest species of the five. The head is longer in 



proportion to the total len_<ftli than in any of the otlier sjiecies; the proportion of 
greatest breadth to length is about the same as in vulgaris and variegnta. But the body 
is considerably narrower towards the tail than in either of the other species. The range 
for the dorsal fin-rays in the above specimens is 69-77 ; Day gives 65-72. The range 
of number for the anal fin-rays in the above table is 53-63; Day gives 50 to 50. 
Day gives the lateral line scales as 72 ; the range in my specimens was 62 to 68. 

Fins. — The dorsal fin commences nearer to the mouth than in any of the other 
species ; the base of the first ray being on the very apex of the snout, on a level 
longitudinally with the U2){)er border of the ventral eye. The jiectorals are as in 
variegata rudimentary ; the right is contained al)Out 4^ times in llie length of the head ; 
the left is extremely minute. 

Eyes. — The dorsal is one-half its longitudinal diameter in front of the ventral and 
less than its diameter from the edge of the snout ; they are very close together, the 
distance between them eipial to half tlie longitudinal diameter of either. 

Nostrils on the right side in their usual position, the posterior short and s:nall, the 
anterior tubidar and long ; on the left side similar to those of variegata. 

Mouth strongly curved downwards as in vulgaris; snout rounded as in tliat 
species. 

The villi on the lower side the snout are arranged in the same manner as in 
variegata. 

The scales absolutely are smaller than in either of the other species, though, as shown 
by the number of scales in the lateral line, they are in proportion to the length of the 
body lai-ger than in the other sj^ecies ; and they are not so broad in proportion to their 
length as in variegata. One of the scales from the middle of the body has 21 rows of 
spines, 4 spines in each of the middle rows (PI. XIV, 5). 

No branches of the lateral line are visible externally on either side of the head. 

Colour. — It is curious that, although in the character of its pectoral fins and of the 
villi of the lower side of the snout, this species closely resembles viriegata, its markings 
are almost the same as those of rnlg'tris. In other words, there is here no correlation 
between the marking and other characters. 

The ground colour of the right side during life is a dull reddish-brown. On this 
ground there are dark brown spots arranged as in n/ljiaris ; there are three principal 
longitudinal rows of these, of which the central row contains usually five spots, the 
dorsal and ventral rows seven or eight. Alternating with the brown spots are light 
blue ones representing the white spots of vulgaris. There are also two interniediate 
longitudinal rows of dark spots, lint the markings of the dorsal and anal fins differ 
considerably from those of vulgaris ; these fins show no longitudinal bands of (-olour, 
but numerous narrow transverse stripes, each sixth or seventh ray being coloured a 
deep black ; the rest of these fins has a yellowish colour which is deepest towards the 
base of the fins. The anterior part of the head is free from spots, the tail has a little 
black at its middle third. 



31 

This species was first recognised as disliuct in Britain Ijy raniell, wliu described it in 
tlie "Magazine of Zoology and Botany," Vol. I, 1837, under the name Monochirus 
rtdnutus. He believed that it had never been described before, and therefore "ave it 
the name minutus. pLcing it in Cuvier's sub-genus JiJonochirus. He gives a figure of 
it, and mentions as its specific character that every sixth or seventh ray of the dorsal 
and ventral fin is black ; he obtained his specimens at Brixham from the travi^lers. 
W. Thompson in the "Annals of Natural History," Vol. II, 1839, identified Parnell's 
species minutus with that mentioned by Cuvier in the " Ivegne Animal," under the name 
Linguatida, which is the Solea parva sine lingu/a of Eondelet. Cuvier defines the 
Monochires as those specimens of Solea in which the pectorals are minute, the left 
being either very minute or altogether wanting. 

I have consulted a French translation of Ivondelet's original Latin work ; this trans- 
lation is dated "Lion " (Lyons), 1558. The names here given are La petite Sole, and 
Solea lingula, and though no characteristic specific features are mentioned in the 
description, the figure given agrees very well in shape with specimens of the present 
species ; this figure shows the left side of the fish. 

Yarrell introduced a figure and description of Parnell's AlonochiruH minutus into his 
supplement to the first edition of his " British Fishes," not having been acquainted with 
the species when he published the book. 

Parnell's species was described as distinct by Dr. Gunther in the British Museum 
Catalogue, under the name Solea minuta from two specimens, one, a dried skin, from 
Yarrell's collection, the other, stuffed and dried, from Brixham. 

Moreau, in his " Poissons de la France," 1881, in describing Microchirus luteys, the 
Solea lutea of Bqnaparte, suggests by means of a note of interrogation that Solea minuta 
is a synonym of that species, and Francis Day, in his " Fishes of Gfeat Britain and 
Ireland," states without reservation that the two species are identical. 

Dr. Glinther in his Catalogue describes one specimen of Bonaparte's Solea lutea. He 
has informed me that he now considers the two species to be identical, and after 
examination of English specimens and Mediterranean specimens of lutea at tlie British 
Museum, and comparing them with the various descriptions, I h^ve no doubt myself 
that lutea and minuta are the same species. 

This spepies was first described by Eissq, in his "Ichthyologie de Kice," under the name 
PleuronerAes luteus, and his description is sufficiently accurate for its identification. 
The same author, in his " Histoire Naturel de I'Europe Meridionale," placed the species in 
the genus Rhoinhus, calling it Rhombus luteus. Bonaparte, in Ins " Faipa Italica," gives 
an excellent description, and two very good coloured figures. He describes the colour 
of the body, apart from the fins, as a uniform golden yellow without spots, Ijut in 
Mediterranean specimens in the British Museum I found the markings which I have 
described above in English specimens. 



32 



CHAITER VII. 
SOLEA GREENII, Guntiier. 

" Solea Greeuii," Giinther, 1889, Ann. Mag. Nat. Hist., vol. iv, No. 2-1. 

Length Lennjtii 

Sex, female. Total length, 19 cm. (/ Jj in.), ■y^^^-^ = over 3^. ^^^ = 6^. 

D. 81. A. 67. C. 19. Pt. 4 r. 2 1. I'v. 5. LI. 138. 

The above are the characters of a single specimen obtained by Mr. Bourne, Director of 
the Plj-mouth Laboratory, by the trawl on board H.M.S. "Eesearch," on July 13, 1889, 
in long. 49° 5' N., lat. 11° 14' W., at a depth of 217 fathoms. 

The characters of the species are, as Dr. Giinther points out, intermediate between 
those of vulgaris and variegata. The filaments on the under side of the head are 
uniformly distributed as in vulgaris, but there is a series of transverse rows of such 
fdameuts along the whole length of the lateral line on the lower side, a character I 
have not seen in any other species. The pectorals are rudimentary as in variegata. 
The cephalic curve of the lateral line runs backwards before turning forwards. In 
colour the upper side is an almost uniform brownish-grey in spirit ; but there are 
also dark blotches or large spots ; there are six of these along the dorsal edge of the 
body and five along the ventral ; also two along the lateral line posteriorly ; these two 
with two dorsal and two ventral spots form two almost continuous transverse bands ; 
another interesting transition from vulgaris to variegata. The outer half of the 
longitudinal fins has also a good deal of black pigment. 

The ground where Mr. Bourne's specimen was taken was a fine grey sand containing 
Foraminifera. Mr. Green also obtained only a single specimen from a depth ui 
l.)0 fms. 47 miles west of Bull Eock off Balinskellys Bay. 

Thus this species lives just beyond the 100-fathom line in llial \)a.vt of the Atlantic 
which lies S.W. of Ireland. 



Part II. 



MORPHOLOGICAL 



m 



CHAPTER I. 

THE OSSEOUS SKELETON. 

The whole body of the sole is covered by the skin, which as everyone knows is so slightly 
attached to the parts beneath it that it can be stripped off as a definite continuous 
membrane. Beneath it is found the flesh, wliich consists of the muscles, by the 
contraction of which all the movements of the fish are produced. The muscles are 
attached to the bones which together form the skeleton. In the middle region of 
the body on the ventral side is a cavity with smooth walls, within which are contained 
the entrails, or viscera, consisting of the organs of digestion, excretion, and 
reproduction. The principal organ of digestion is the digestive tube which leads from 
the mouth and after various convolutions opens to the exterior again at the vent or 
anus. The organs of respiration or gills are fringes supported on rods between which 
are slits or clefts by which the cavity of the throat opens on each side into a gill 
chamber. Each gill chamber again opens by a single aperture to the exterior. The 
blood vessels ramify in the substance of aU the organs now mentioned, but the heart 
which keeps the blood moving in circulation is contained in a special cavity which is 
separate from that containing the viscera. The skin and the membrane lining the 
digestive tube become continuous with one another at the mouth and anus, and at the 
gill-clefts. The nerves also ramify in the substance of the muscles and other organs, 
but, excepting the sympathetic system, they all radiate from the brain and spinal cord 
which are contained in a chamber on the dorsal side of the skeleton, the brain being 
contained in the cavity of the skull, the spinal cord being enclosed by a series of 
arches formed by processes of the spine. Some of the nerves convey the impressions 
received by the senses to the brain, and may be regarded as proceeding from the sense 
organs to the brain ; the principal sense organs are the skin, the e3'es, the ears, and 
the olfactory organs. The other nerves conduct impulses from the brain and spinal 
cord to the muscles and other organs causing the former to contract and regulating 
the functions of the latter. 

The structure and relations of these various organs can be made most easily 
intelligible by describing the skeleton first. 

The Skull. — -The central part of the skeleton consists of tlie skull and the vertebral 
column, the latter being composed of a longitudinal series of distinct bones, the 

F 2 



86 

vertebras: the skull here meaus the bony structure which coiitaius the braii>, and 
supports the eyes, ears, and olfactory organs, and which remains as a united whole 
when the soft parts of the head of the fish are removed by boiling or otherwise. The 
form of the skull is shown by four drawings of it on Plate XI (Figs. 5-8). It consists of 
two main portiou.s. The posterior and larger portion has a somewhat cylindrical shape, 
and encloses a cavity m which the brain lies in the entire fish, this is the cranial 
portion ; the anterior or facial portion does not enclose a cavity, but may be said to 
consist of three separate processes from the brain-case which unite together at their 
anterior ends. One of these processes is (apparently) on the right side of the head of the 
fish and separates the eyes from one another ; it may be called the interorbital septum, 
the not very definite concavities on either side of it in which the eyes lie being the 
orbits. 

If the skuU is placed in the position it occupies when the entire fish is held vertically 
upright on its ventral edge, that is in the same position in which a symmetrical fish 
swims, the cranial portion of the skull will be seen to be almost perfectly symmetrical 
while no symmetrj- is visible in the facial portion. Comjjaring the cranial portion 
with the corresponding part of the skuU of a symmetrical fish, we can recognise in its 
walls the same bones as in the latter, the walls being made up of these bones firmly 
united at their edges. These edges are usually irregularly toothed so as to fit into 
each other, and the lines of junction are called sutures. The sutures can be traced out 
with care in the entire cranium, Init where they are obscure the exact limits of the 
component bones can be found by boiling the skull and pulling the separate bones away 
from one another. The outlines of these bones are indicated on the figures of the 
skull. Tlie auditory organs in the entire fish are situated within the convex side walls 
of the cranial portion, and the bones of this part have names with the suffix "otic," 
implying their relation to the ear. 

The back of the cranial portion is called in all vertebrates the occiput and the bones 
of this part occipital bones. In this wall of the cranium is a large circular aperture, 
the occipital foramen, through which the spinal cord is continued forwards into the 
brain. Below the occipital foramen is a solid bone witli a conical depression in its 
posterior surface, this is the basi-occipital, and the depression marks the place where 
the first vertebra is attached to the skull. At the sides of the occipital foramen 
inferiorly are the two ex-occipital bones, ex.o., one on each side. Above these, reaching 
to the upper edge of the foramen, are two large somewhat convex bones, the epiotics, ep.o. 
On the dorsal surface of the skull there is in the centre a large median flat bone, the 
supra-occipital, s.o., whicli in many vertebrate skulls extends to the edge of the occipital 
foramen, but is here separated from it by the epiotics. On either side of the 
supra-occipital is a parietal bone, pa. In either lateral wall of the cranium, adjoining 
the edges of the ex-occipital, epiotic, and parietal, there is a somewhat large Ijone 
having a rugged process projecting outwards ; this is the pterottc bone, pt.o. In front 
of this is a shghtly smaller square bone, the sphenotic, sp.o. Between the pterotic 



37 

and (he basi-occipital is a small square bone, the ojjisthotic, op.o., and in front of this 
below the sphenotic is the prootic, pr.o. 

Adjoining the edges of both prootics and sphenotics, and attached behind to the 
basi-occipital, is an elongated keeled bone which projects forwards to form the ventral 
process of the facial portion of the skull : this is the jmrasphenoid, pa.s ; its posterior 
portion forms the anterior part of the floor of the cranium. Attached to the ventral 
surface of the parasphenoid is a bone which is elongated dorsally and projects 
ventrally into a cylindrical knob ; this is the vomer, vo. The interorbital septum is 
formed by the anterior processes of two bones whose flat posterior portions are nearly 
symmetrical and form the anterior part of the roof of the cranium, attached behind to 
the edges of the supra-occipital and parietals. These are the frontal bones, r.f., l.f. 
These bones are, as compared with the corresponding bones of the skull of a 
symmetrical fish, the most distorted of all the bones in the skull of the sole. In a 
symmetrical fish the frontal bones are perfectly symmetrical, and their anterior parts 
lie above and between the symmetrically placed eyes. In the sole also their anterior 
processes are between the orbits, but have been twisted round through an angle of 
90°, so that the middle line of the dorsal surface of the cranium when produced 
forwards does not pass between the frontal bones, but a line drawn in a longitudinal 
direction over the right surface of the cranium, across the pteroic aud sphenotic bones 
does pass between their anterior processes. This shows that the dorsal eye of the sole 
is really the left eye, and that the eyes and orbits with the interorbital septum have, 
as compared with those of a symmetrical fish, been twisted round through an angle of 
90° while the cranial portion of the skull remained stationary. Connecting the 
inferior process formed by the parasphenoid and vomer with the interorbital septum 
anteriorly is a single bone having a somewhat hooked process in front — the mesethmoid, 
raes.e. Attached to the mesethmoid posteriorly on the left side, and joined also to the 
parasphenoid, is a large flat bone concave towards the right, the left ectethmoid, ect.e. 
A posterior process of this bone unites with an anterior process of the left sphenotic to 
form the third process of the facial region of the skull. The right ectethmoid is a small 
ring-shaped bone attached ventrally to the anterior end of the frontals and to the 
mesethmoid. 

Between the origins of the three facial processes the cranial cavity opens anteriorly 
by a wide aperture. There is a large round foramen in the left ectethmoid, leading 
from the left orbit to the external surface of the facial part of the skull. On the upper 
surface of the cranial portion there is a small foramen in the flat posterior portion of 
each frontal bone, the left foramen being larger than the right. At the anterior and 
inferior edge of each sphenotic bone there is a considerable indentation, which, with a 
corresponding indentation in the edge of the parasphenoid, forms a large foramen, the 
sphenotic foramen. That of the left side is twice as large as that of the right, and in 
front of the former are two small foramina which are absent on the right side. 
Through each prootic bone is a smaller foramen, the prootic foramen ; the left of these 



38 

is a little larger than the riglit. In the posterior part of each opisthotic bone is a 
minute opisthotic foramen. In each ex-occipital there is a considerable foramen 
directed downwards, and behind this a minute foramen directed outwards. 

It now remains to call attention to the form of the outer surface of the skull. The 
pterotic process projecting outwards from the pterotic bone has already been 
mentioned. A similar but longer and flatter process projects from the sphenotic 
bone above the sphenotic foramen ; these processes serve for the attachment of muscles. 
Below these two processes are two smooth depressions in which are articulated the two 
heads of the hyomandibular, a bone which is connected with the jaws and branchial 
apparatus. In the centre of the supra-occijiital bone is a somewhat elongated crest. 
At each side of the dorsal surface of the skull posteriorly is another crest longitudinally 
directed, formed partly from the pterotic, partly from the parietal bone : this may be 
called the parietal crest ; the one on the right is larger than that on the left. These 
crests also serve for the attachment of muscles. At the anterior part of the basi- 
occipital bone are a pair of conical prominences with their broad bases downwards : 
these are continuous with one another in the median plane. The left ectethmoid bone 
sends ofl" a curved process towards the right side. 

The Vertebral Column. — Any one of the vertebrse from the middle third of the spine 
consists of a somewhat cylindrical central mass, the centrum, and two elongated 
processes or spines, a dorsal and a ventral. The centrum has the form of two truncated 
hollow cones placed with their narrower ends towards each other and united together 
by a solid disc. The conical hollow at the anterior and posterior surfaces of each 
centrum with the corresponding hollows of the adjacent vertebrae, enclose cavities 
which are filled by an elastic gelatinous tissue. The lateral depressions at tlie right 
and left sides of the centrum are each divided by a longitudinal ridge of bone. The 
dorsal spine really consists of two hollow bony tubes which diverge at their bases, 
where they are united with the centrum towards the anterior edge of its dorsal surface, 
and which are united firmly together in the median plane of tlie fish's body for tlie 
greater part of their length. The diverging legs of the spine form a pointed 
arch, and through the series of these arches runs the spinal cord, wliicli is thus 
protected from pressure by the bony arches. The leg of the spine on each side of the 
vertebra is expanded longitudinally where it joins the centrum, and in this expanded 
part are two foramina, through which the ventral and dorsal roots of a spinal nerve 
pass. The ventral spine of the vertebra has a similar structure, but the arch between 
its legs is larirer, and through the series of these arches run blood vessels. There are 
50 vertebraj altogether, and the 11 ih to the 50th have tlie structure now described. 
The dorsal and ventral processes in all these are very long, four to five times as long as 
the centrum. In the first of these vertebnc the spines are almost at right angles to 
the centrum, but towards the posterior end they slope more and more backwards. 
The spines increase in length slightly towards the centre of this region, and again 
decrease slightly at the posterior end. The centra become longer and narrower 



II 



39 

towards the posterior end. "Behind the last of these vertebras are bones which 
terminate the vertebral column : these consist of a central fan-shaped bone, the anterior 
end of which is shaped like the anterior part of a vertebra, and is connected with the 
posterior face of the last vertebra by membrane, and two other flat bones, dorsal and 
ventral to the central one. The central bone expands posteriorly in the median plane 
of the body into a triangular plate, which is partially divided by radiating furrows into 
a number of rods. These rods are known from their development to represent the 
ventral spines of a number of vertebrae fused together into the fan-shaped bone. The 
flat bones dorsal and ventral to the fan-shaped bone are similarly divided, but are much 
narrower : these are obviously also dorsal and ventral s})ines of the more anterior of 
the vertebra3 represented by the fan -shaped bone. The rays of the caudal fin articulate 
with the ends of these rods (PI. X). 

The ten anterior veriebrte differ considerably from the posterior 40. All of them 
have dorsal spines except the first : these spines resemble those of the vertebrae already 
described, except that they become thicker and shorter and more inclined forwards 
towards the anterior end. The dorsal spine of the second vertebra leans forward so 
much that it is in contact with the posterior face of the skull. The fifth to the tenth 
vertebra have ventral spines also, but these are of rapidly decreasing length from the 
tenth to the fifth, and are also much inclined backwards. The first four vertebraj 
have no ventral spines. The second to the eighth vertebraj, seven in all, bear very 
slender short ribs which are not processes of the vertebrte, but separate bones which 
articulate with the centra at the upper side of their lateral ridges. The first vertebra 
is rudimentary : its centrum is very narrow antero-posteriorly, and it has two small 
dorsal processes which lie along the front edge of the base of the dorsal processes of 
the second vertebra, but do not unite to form a spine. 

The centra of all these vertebrae are united together in the following way. The 
posterior face of each vertebra has, as we have seen, a conical depression or cavity : the 
rim of this cavity is united firmly to the corresponding rim on the anterior face of the 
succeeding vertebra by strong tough membrane, which is continued over the surface of 
the vertebras, which is in fact i)art of the periosteal membrane. The closed cavities 
formed by the juxtaposition of the conical depressions are filled by a firm elastic 
gelatinous tissue which forms so many elastic pads b9tween the centra. The connection 
of the ex-occipital bone of the skull with the first vertebra is of the same kind as that 
between adjacent vertebrae. 

Closely connected with the vertebral column is the system of bones which forms the 
framework and support of the median fins. Placed like the vertebral spines in the 
median plane of the body and extending outwards from the ends of those spines are a 
great number of bones shaped somewhat like paddles. These are the intcrspinovs hones. 
Each consists of a long slender shaft and a broad head expanded in the median plane 
They are placed with their shafts towards the vertebrte, their heads projecting 
outwards. The ends of the shafts lie alongside the ends of the spines of the vertebra 



40 

in the intervals between the spines, hence the name of these bones. There are usually 
two interspinous bones between two adjacent vertebral spines, never more than two, 
but in many cases only one : one interspinous bone, in Fig. 1 on PI. X, has two shafts 
to a single head, the end of a vertebral spine lying between the two shafts. In the 
middle region of the body each interspinous bone has a small wing-like expansion on 
each side of the shaft just below the head. On the dorsal side the interspinous bones 
are perpendicular to the vertebral column at about one-fourth of the whole length 
from the anterior end of the body : from this region to the tail they slope more and 
more backwards ; from this region forwards they slope more and more forwards. In 
front of the dorsal spine of the second vertebra there are three short stout interspinous 
l:)ones whose inner ends lie close to the middle dorsal line of the cranial portion of the 
skull. In front of these is a large curved spine-shaped bone pointed at its outer end, 
stout and l)luiit at its inner, which curves forwards almost parallel to the axis of the 
skull. To the dorsal side of this bone are attached two short interspinous bones. 

On the ventral side the interspinous bone in front of the ventral spine of the eleventh 
vertebra is almost perpendicular to the vertebral column: from this point to the tail 
region the interspinous bones slope more and more towards the posterior end. In 
front of the same interspinous bone there is one other free interspinous bone slightly 
inclined forwards, and in front of this is a stout curved cylindrical boTie, which 
terminates the series anteriorly and forms the posterior boundary in the median plane 
of the main body-cavity of the fish. This cylindrical bone bears four shortened 
interspinous bones which are inclined forwai'cls and are successively shorter and shorter, 
the most anterior being merely a small head without a sliaft. 

The fin-rays of the dorsal and ventral median fins, of the dorsal fin and anal fin as 
they are usualh' termed, are not articulated directly with the outer ends or "heads " 
of the interspinous bones : to these heads are attached a series of nodules of cartilage, 
elongated from before backwards, and somewhat cylindrical in shape. Except in a 
certain region each of these nodules is situated between two adjacent heads of 
interspinous bones, attached to both of them. The region excepted is the anterior 
part of the dorsal series, where one nodule is attached separately to each head. 

The fin-rays have the following structure. Each ray is compound and constructed 
somewhat in the same fashion as a vertebral spine. It consists of a right and left half, 
which are separate and divergent at their inner ends, attached together in the median 
plane of the fish for the outer seven-eighths of their length. The divergent ends embrace 
one of the cartilaginous nodules previously described, Ijestriding it as a man bestrides a 
saddle, and are attached to it by fibrous membrane in this position. One of the halves 
of the fin-ray thus belongs to the riglit or coloured side of the fin, the other to the left 
or white side. In consequence of the mode of attachment described, the fin-ray can 
only move on the cartilaginous nodule backwards and forwards : as a matter of fact 
its motion is limited between a jiosition in which it is perpendicular to the longitudinal 
axis of the fish, and a position in whicli it lies inclined backwards from its attached 



41 

base, and almost parallel to the axis of the fish. The outer part of the fiii-ray formed 
of the two united lateral halves bifurcates in an antero-posterior direction into two 
divergent branches. Thus the outer half of the lin-ray consists of two diverging 
branches both in the plane of the fin, one anterior and one posterior, but each of these 
is made up of two lateral halves glued as it were together lengthwise. Thus if a lin- 
ray is separated, and a knife passed between the diverging right and left legs of the ray, 
the whole ray can be easily divided into a right half ray and a left half ray, and each 
of these is forked at its outer half length into two branches. The basal portion of the 
fin ray is solid, but the outer five-sixths, including the two forked branches, consist of 
a series of short cylindrical bony pieces united by flexible membrane. Thus tlie ouler 
part of the fin-ray resembles somewhat the series of vertebral centra on a small scale 
and without the spines, if we suppose the series of centra after being single for a 
certain length to branch into two series having the same structure. 

The tail fin-rays resemble those of the dorsal and anal fins in general structure, but 
are more branclied : in them each of the two original branches divides again into two, 
and some of these again into two : the branching of the ray is always dichotomous, 
that is, a branch when it divides splits only into two smaller branches, but of the four 
secondary branches all do not always divide : thus the fin-ray terminates in seven or 
eight branches spread out like a fan. The caudal fin-rays are not in connection with 
either interspinous bones or cartilaginous nodules, but are articulated directly to the 
terminal bones of the .vertebral column, and to the spines of the last vertebra. 

The skeleton of the paired fins is closely related to that of the branchial region and 
will be described in connection with it. 

The Jaws and Branchial Arches. 

We have now to consider the bones of the jaws and branchial arches, and other 
bones connected with the skull. The more superficial of these bones are shown in 
Figs. 1 and 2, PI. XI. The bones of the right side. Fig. 1, differ considerably in size 
from those on the left, although in their relations the bones of the two sides correspond 
to one another. The bones of the right side are as follows. The two sockets in the 
side of the cranial portion of the skull, in the pterotic and sphenotic bones, contain 
the two rounded heads of a flat elongated bone which extends downwards and 
somewhat forwards. This is the hyomandibular, hm. To the lower end of this bone is 
attached a system of flat bones which projects horizontally forwards into a smooth 
knob with which the lower jaw is articulated, and sends off upwards and forwards a 
flat band of bone, the end of which is again attached to the skuU at the side of the 
vomerine projection. At the posterior border of the hyomandibular and the system 
of bones just mentioned is a crescent-shaped bone, which is firmly attached to the 
others and acts like a splint, binding them rigidly together. This is the jireopeiriilar, \)o. 
The separate bones of the system connected with the lower end of the hyomandibular 

G 



42 

are as follows. Directly attached to the end of the hyoinaudibular is seen the end of 
a bone which passes downwards beneath the preoi^erculum out of sight, and is 
connected with the system of branchial arches which occupy a deeper position. This 
is the stylohyal. Anterior to this is a flat bone which projects into the quadrate in its 
under surface, this is the si/mplectic, s. Dorsal to this is a flat somewhat concave bone 
with a triangular outline, the metapterygind, mt. The triangular bone, which is at the 
anterior end of the series, and which supplies the rounded head to which the lower 
jaw or mandible, m., is articulated, is the quadrate, q. Running upwards from the 
quadrate dorsally are a pair of splinter-like bones, the anterior of which is the 
jHerygoid, pt., and the posterior the mesopterygnid, ms. Connecting these with the 
skull at the side of the vomerine process is the palatine, pa. It will be seen that all 
these bones are somewhat larger on the left side. Fig. 2, than on the right, Fig. 1. 
The superiority is especially well marked in the pterygo-palatine bar, which is broad 
and strong on the right, narrow and delicate on the left. 

Attached to the posterior edge of the hyomandibular and preopercular is the oper- 
culum, which is chiefly composed of the three bones,o.,io., so. : these are the opercular, o., 
which is articulated to a knob jjrojecting downwards on the posterior side of the 
head of the hyomandibular, the intenqurcular, i.o., and the sub-ope rcular, s.o., which 
are only held in their places by the fibrous tissue of the operculum. The lower jaw 
is called the mandible, which consists of three bones, the articular, angidar, and dentary, 
fltted and firmly united together : the upper jaw consists of two bones, the maxilla,x, 
and the prema.villa, p x. All these bones are much smaller on the right or ujjjjer side 
of the head than on the left or lower ; this is especially true of the maxilla and 
premaxilla which, as the figures show, are almost rudimentary on the right side, and 
very large on the left. On the left side the maxilla is entirely excluded from the edge 
of the lip ; on the right side its posterior process forms part of that edge. The 
mandible on the right side has the form of an elongated bar, on the left side it is a 
broad triangular stout plate, the dorsal edge of which is strongly convex and bears a 
patch of rod-like teeth, biting against a concave larger patch of similar teeth in the 
premaxilla. On the left side the end of the premaxilla articulates with a knob on the 
mandible, an arrangement which makes the bite much more effective ; on the right side 
there is no such articulation. The two mandibles are firmly united together anteriorly 
in what is called the symphysis of the mandibles. The anterior ends of the maxillie 
and premaxilla:^ are all firmly united together and to the lower side of the mesethmuid 
bone by fibrous membrane. 

If we now dissect away all the bones above described except the hyomandibular, 
we find the bones of the branchial a])paratus lying beneath them as shown in Plate XI, 
Fig. 3, from the right side. The gills themselves are vascular fringes which project 
outwards and backwards from a series of bars ; between these are the clefts by which 
the water passes from the cavity of the throat to the gill chamber and so to the exterior. 
These bars are called the branchial arches, from their curved shape, and each bar is 



I 



43 

supported by a series of bones called a (bony) branchial arch. Tlie first of these arches 
is different from the rest, and is called the hyoid arch. It is attached to the end of the 
hyomandibular, and consists of, 1st, the small cylindrical bone, marked 2 in the figure, 
and called stylo-hyal; next, two broad stout bones placed end to end, 3 and c.h. in the 
figure, the epi-hyal and cerato-hyal ; and finally, two cubical bones placed side by side, 
the hypo-hyals, h.h. Between the hypo-hyals of the opposite sides is inserted a bone 
which is flattened in the median plane of the fish's body : this is usually called the 1st 
basi'branchial, although in the sole it is connected only with the bones of the hyoid 
arch. Above it is a cylindrical bone called the basi-hyal or entoglossal, b.h. 

Attached to the lower edge of the epi- and cerato-hyals are a series of long bones like 
curved spines, 3 to the epi-hyal, and 4 to the cerato-hyal. These are the hranchiostegal 
rays, and they support a curved membrane which extends inwards from the inside of 
the lower edge of the operculum, and in ordinary respiration closes the lower part of 
the opercular aperture. 

The 1st branchial arch is composed of a chain of bones of which the most dorsal 
attached to the side of the keel of the parasphenoid bone is the pharyngo-hranchial, 8, 
next to this is the ejn- branchial, 9 : these two are directed downwards and outwards, but 
the cerato-branchial, c.b. 1, which succi^eds, passes inwards and forwards; it is followed by 
the hypo-branchial, which is joined to the median 2nd basi-branchial, b.b. 2. The other 
arches, four in number, exhibit a similar plan of structure, but the last is much reduced. 
The pharyngo-branchials of the 2nd, 3rd, and 4th arches are not styliform, like that of 
the first, but are broad and flat; the 3rd and 4th are fused together, the 2nd is united 
to them, and all three bear teeth on their lower suifaces and form together the npper 
pharyngeal bone. The second hypo-branchial is articulated with the third basi- 
branchial, and the third hypo-branchial comes into slight connection with the posterior 
end of the same median bone. The two hypo-branchials of the fourth pair of arches 
are fused together to form a rhomboidal cartilage in the middle line behind the third 
basi-branchial. The fifth arch is represented only by a cerato-branchial on each side, 
which meets its fellow in the middle line ; these two bones bear teeth on their upper 
surface, and being situated in the ventral wall of the throat they bite against the upper 
pharyngeal teeth, forming a second masticatory apparatus ; these bones of the fifth 
arch are usually called the lower pharyngeals. The relations of the hyoid and branchial 
arches of the opposite sides are shown in Plate XI, Fig. 4 where they are seen spread 
out with their internal surfaces upwards. 

The pectoral and pelvic fins on each side are attached to the posterior border of a 
bony arch which extends from the back of the skull downwards, curving first back- 
wards and then forwards, and meeting its fellow of the opposite side at the ventral 
edge of the body. This bony arch forms the posterior border of the opercular cleft. It 
consists of the following bones : 2i. post-temporal, 25, Fig. 3, which is forked anteriorly and 
attached by membrane to the posterior wall of the skull, the upper branch of the fork 
being connected with the epiotic, the lower with the opisthotic ; a supra-clavicle, 26, an 

G 2 



44 

elongated bone joined on to the lower end of the post-temporal, a clavicle, 27, which curves 
forwards, and is shaped like a trough the cavity of which is posterior, the trough being 
V-shaped in section. The clavicle is connected at its lower end, in the median ventral 
line, with its fellow of the opposite side. 

The pectoral fin is supported by a flat basal plate attaclied within the upper part of 
the trough of the clavicle ; this plate consists of two bones united by cartilage ; the 
upper of these, 29, is the scapula ; the lower, 30, the coracoid. The pectoral fin-rays 
are articulated to the posterior cartilaginous edge of this basal plate directly as the 
caudal fin-rays to the fan-shaped terminal bone of the vertebral column. 

The pehic fin is similarly supported by a triangular single bone, 31, which is attached 
to the lower end of the clavicle. It is usually called the pubic bone, thougli it is 
probably homologous, not with any part of the pelvic arch of Elasmobranchs, but 
with the basal cartilages of the pelvic fin in those forms. 

A flat bone in the median plane extends forwards from the junction of the clavicles 
to the lower edge of the first basi-branchial. This bone, marked 28 in Fig. 3, has been 
called the urohyal by Huxley, basi-branchiostegal by Parker, but has really nothing 
to do either with the hyoid arch or the branchiostegal membrane ; it is better to call 
it simply the iwjuhir bone. Posteriorly it sends off a pointed ventral process, while 
the anterior three-fourths of it form a band of uniform width. 



45 



CHAPTER II. 

THE FIBROUS MEMBEANES AND MUSCUL.1TUEE. 

The Fibrous Membranes, 

All the bones of the skeleton now described are bound together by strong fibrous 
membranes. . In the median plane a tough membrane of this kind extends from bone to 
bone everywhere except in the median visceral cavity, so that the whole body of the fish, 
excluding the region of this cavity and the ventral region of the head, is divided into 
two lateral similar halves by a continuous partition consisting of a tougli membrane 
supported by the bony framework. The structure of this partition in fact resembles 
that of one of the screens often used in our rooms to keep off draughts, the bones 
corresponding to the wooden framework, the membrane to the canvas stretched over 
it. But there is in the organic structure a more intimate connection between the 
fibrous membrane and the bony framework. Every bone is clothed externally by a 
tough fibrous membrane, the periosteum, and this is actually continuous with the 
membrane which connects the bones together. The whole structure is as it were a 
continuous deposit in which certain parts have been differentiated by the deposition 
of calcareous compounds and structural modification to form bone. Yet, tough and 
strong as the fibrous membrane is in its natural state, firm as it is found to be when 
the muscles are dissected away in the dead fish, if the fish is boiled for a short time it 
dissolves, and the bones all fall asunder. The reason of this is that the basis of the 
material of which the fibres consist is gelatine, and therefore though they retain their 
strength and structure during life, or in cold water, when subjected to the action of 
boiling water their structure is destroyed and they become simply a mass of soft liquid 

jelly. 

The median fibrous membrane is continuous laterally with other membranes which 
are placed at right angles to it and connected with the vertebrae and interspinous 
bones. These lateral membranes run between the various muscles, which are attached 
to them, and externally become continuous with the derma, or deeper fibrous layer of 
the skin. The principal of the lateral membranes on each side runs longitudinally 
along the centre of the vertebraj from the skull to the tail, and extends outwards to 
the skin, thus dividing the muscles of each side of the body into a dorsal and a ventral 



46 

half. Shorter membranes transverse to this divide the muscles again into a series of 
oblique flakes which are seen separating from one another in a boiled fish brought to 
table. 

In a symmetrical fish the median skeletal partition formed by the vertebras and 
their spines and the interspinous bones terminates at the back of the skull, but in the 
sole it is extended still further anteriorly over the dorsal side of the skull to the 
extremity of the snout. The attachment of the membrane to the skull runs at first 
along the median dorsal line of the skull, that is, the morphological median line, but 
anteriorly it runs to the left of this line. It crosses the base of the left frontal bone 
and is continued alcng the edge of the larse left ectetlimoid and finally to the left edge 
of the mesethmoid. '.riius, morphologically, the median skeletal partition is continued 
forwards on the left side of the facial region ventral to the left eye, though actually 
the anterior continuation is in the same plane as the main part of the partition. This 
anterior continuation is of course due to the anterior development of the dorsal fin 
Avhich is supported by it. 

Mtisculaiure. 

A general view of the muscles of the right side of the sole is given on Plate XII. 

The white parts in that draAving represent the white tendinous membranes, excepting 

some of the bones of the head which are smoothly shaded, and the fin-rays : the 

shading of fine lines indicates the muscles, the lines being drawn in the direction of 

the muscle-fibres. The principal muscles of the body are the great lateral muscles, 

one dorsal and one ventral, separated from one another by the longitudinal fibrous 

membrane already described as projecting from the centra of the vertebrae outwards 

to the skin. Each lateral muscle consists of a longitudinal series of folded plates or 

segments, separated from one another by the transverse membranes previously 

mentioned. The fibres in the muscle-segments run in an antero-posterior direction 

parallel to one another, and are attached at each end to the transverse membranes, or 

to the bones and membrane in the median plane of the body. The transverse fibrous 

membranes have a curious folded and twisted arrangement. The outer edge of each, 

as can be seen from the illustration, has the form of the letter S. Starting from the 

longitudinal lateral membrane it curves first anteriorly, tlien posteriorly, and finally 

runs anteriorly again, tluis forming two curves in opposite directiims and a larger outer 

portion running obliquely forwards. The membrane itself is deeply hollowed 

forwards in the region of the first curve, backwards in that of the second, so 

t' .at the inner edge of tlie membrane instead of being S shaped is Z-shaped. This 

inner edge of the transverse membrane is attached to the median bones and membrane 

in the following way : it runs first along a vertebral spine for a short distance, then 

suddenly turns ofT at an angle and runs directly backwards till it reaches the next 

spine behind, along which it runs outwards (dorsally or ventrally) for some distance, 



47 

and then again leaves that spine and runs obliquely forwards. Thus each transverse 
membrane is attached by its inner edge to two adjacent vertebral spines at different 
parts of its length, and along the rest of its length- is continuous with the median fibrous 
membrane which extends between the spines and the interspinous bones. 

The anterior segments of the dorsal lateral muscle are much elongated and bent 
forwards, so that their separating membranes are attached to the dorsal surface of the 
skull, the anterior interspinous bones and the membrane connecting the latter. 

The anterior segments of the ventral muscle covering the visceral region are straighter 
than the posterior, and the inner edges of the dividing membranes are not attached to 
any firm skeletal structure, but simply to the fibrous membrane which encloses the body- 
cavity, the peritoneal membrane. The ventral part of the ventral lateral muscle on 
each side is also separated from the median skeletal partition by the posterior prolonga- 
tion of the body-cavity. 

The posterior muscle-segments, in correspondence with the greater backward slope 
of the vertebral spines, are folded to a much greater extent than the anterior. The 
terminal segments form a system of muscles which are attached to the bases of the 
caudal fin-rays. 

It follows from the description that in each lateral muscle there are as many muscle 
segments as there are vertebrce, and that each dividing membrane corresponds to a 
vertebra Thus the muscle segments themselves correspond to the junctions between the 
vertebral centra, an arrangement which allows the vertebral column to be bent in all 
directions by the action of the lateral muscles. It is clear that, although it is difiicult to 
understand in detail the effect of the complicated attachments above described in the 
contraction of the muscles, the general effect of the contraction of the lateral muscles of 
one side is to bend the body powerfully towards that side, and it is by this alternate 
bending of the body first to one side then to the other that the sole swims through the 
water when it rises from the bottom, or swims along the bottom. The lateral muscles 
form the bulk of the edible portion of the fish. The lateral muscles of the left or lower 
side do not differ in any important respect from those of the right. 

The other muscles of the sole are the muscles of the fins and the muscles of the 
ventral retjion of the head, and the eve muscles. 

The muscles of the longitudinal fins are well developed and important. The caudal 
fin-rays are, as has been mentioned, moved by muscles which represent the terminal 
muscle segments of the lateral muscles. The dorsal and anal fin-rays are moved by two 
distinct systems of muscles. One system serves to erect the rays and to depress them 
bv causing them to slope backwards till they are almost parallel to the edge of the 
body. The other system moves the rays away from the median plane, either to the right 
side or to the left (upwards or downwards in the natural position of the sole). The 
muscles of the former system may be called the elevators and depressors of the fin-rays, 
those of the other the right and left abductors. The abductors of the fin-rays are 
superficial, lying innnediately beneath the skin ; there is a single muscle on each side 



48 

to each ray. These muscles take their origin from the fibrous tissue which covers the 
lateral muscles and which is continuous with the fibrous layer of the skin. Each 
muscle is inserted into the side of a fin-ray outside its articulation, but the end of 
the muscle also has connections by means of fibrous tissue with the ends of the 
iuterspinous bones. 

The elevators and depressors lie beneath the abductors : there is one elevator and one 
depressor on each side of the body to each fin-ray. In (he greater part of the fins the 
heads of the iuterspinous bones are between the bases of the fin-rays, and each 
elevator lies along the posterior half of the side of an iuterspinous bone, while each 
depressor lies along the anterior half These muscles are considerably smaller than 
the abductors. They are inserted into the bases of the fin-rays in front and behind and 
take their origins from the surface of the iuterspinous bones and intermediate fibrous 
membrane. Their inner ends extend beneath the outer edges of the lateral muscles, 
which are free. The elevators and depressors of the fin-rays are shown in Plate XII. 
along the whole of the ventral side of the body and the anterior part of the dorsal 
side, while the abductors are shown along the posterior three-fourths of the dorsal side. 

The muscles of the rays of the pectoral and pelvic fins are closely similar and require 
no special description. 

The muscles of the ventral region of the head may be classified according to their 
functions into two divisions — the masticatory and the respiratory, the former moving 
the jaw«, the latter the branchial arches. 

The most powerful of the masticatory muscles is the common jaw muscle, which 
partly corresponds to the temporal and masseter muscles in man. Its origin occupies 
the outer surface of the " suspensorium," i.e., the system of bones to wliicli the 
mandible.is articulated, and part of the surface of the skull. It consists of two portions, 
a superficial and a deeper, the former arises from the hj-omandibular and the anterior 
edge of the preoperculum, and from the anterior part of the sphenotic, and from the 
basal portion of the right frontal ; the deeper portion is smaller and arises from the 
metapterygoid, symplectic, and quadrate. Between the two portions runs a large nerve, 
the mandibular branch of the fifth cranial nerve. Both portions of the muscle on the 
right side of the head terminate in a tendinous structure which divides into two 
tendons, the upper is longer and thinner and is inserted into the middle of the posterior 
edge of the maxilla, the lower is shorter and broader and is inserted into the upper edge 
of the mandible, chiefly into the articular bone, a little in front of the articulation of 
the mandible with the quadrate. It is evident that the chief function of this muscle is to 
bring the jaws together, which it does principally by powerfully pulling the mandible 
upwards, while its upper tendon draws the upper jaw downwards and backwards. The 
muscle on the left side of tlie head is somewhat larger than on the right, and is inserted 
only into the mandible, the tendon passing to the maxilla being entirely absent. 

The levator suspensorii is a muscle which arises from the sphenotic, especially from 
the lateral process of that bone, and is inserted into the head of the hyomandibular. 



"49 

The depression of the lower jaw is effected by the paired geniohyoid muscles, each 
of which arises from the external surface of the hypohyal and ceratohyal, and is 
inserted into the inner surface of the symphysis of the lower jaw, that is to say, of the 
junction between the two mandibles of opposite sides. 

From the lateral surface of the parasphenoid passes on each side a broad band of 
muscle outwards to the hyomandibular and pterygoid bones : these are the palatal 
muscles wliich constrict the cavity of the mouth in swallowing. 

Behind the last there are other transverse muscles passing from the side of the skull 
to the inner surface of the hyomandibular and operculum. 

A strong broad transverse muscle passes from the inner surface of one mandiljle 
anteriorly to the inner surface of the other ; this is the muscidus transversus mancHbulce. 
It lies immediately beneath the skin of the floor of the mouth, and assists considerably 
in the biting action of the mandible of the left side. 

Most of these muscles, although chiefly concerned in seizing and swallowin<T food, are 
also used in inhaling water through the mouth for respiration. The followincr muscles 
connected with the branchial arches are almost entirely respiratory. 

The most supei-fici^il of them is the levator operculi, which rises from the ridcre and 
process of the pterotic and is inserted into the head and upper edge of the ojjerculum : 
it raises the gill-cover. 

The gill-arches are raised in inspiration by the levatores arcuum branchialhmi, which 
arise from the inner side of the articulation of the hyomandibular bone with the prootic 
and opisthotic, and are inserted into the outer surfaces of the bony branchial arches 
into the epi-branchial bones. 

Internal to the last are other muscles which pass from the inferior conical process of 
the basi-occipital to the pharyngobranchials of the 2nd, 3rd, and 4th branchial 
arches, that is, to the superior pharyngeal bones. The first pharjaigobranchial bone, 
which is small and slender, lies along the side of the posterior end of the parasphenoid, 
to which it is connected only by connective tissue. 

A powerful muscle posterior to the last passes from the lower surface of the anterior 
vertebrai forwards to the dorsal surface of the superior pharyngeal bones : this muscle 
retracts those bones, and is therefore inspiratory. 

On each side two muscles arise from the anterior surface of the clavicle and pass 
upwards and forwards to the posterior surface of the inferior pharyngeal bone. As 
this latter bone is destitute of gills, and all the gill clefts lie in front of it, its retraction 
assists to open these clefts : these muscles are therefore inspiratory. 

Expiration is effected by all the muscles which constrict the cavity of the mouth and 
throat, the jaws being shut first. In addition to some of those already mentioned the 
following, which bring the branchial arches into contact with one anotlier, are expiratory. 

Transverse muscles between the two inferior pharyngeal bones, and between the 
cerato-l)ranchials of the 4th branchial arch. 

Transverse muscles between the superior pharyngeal bones. 

H 



50 

A strong flat muscle on eacli side which arises from the lower end of the clavicle 
and is inserted into the sides of the jugular bone. 

Small muscles between the upper and lower extremities of the branchial arches. 

The eye muscles in tlie flat fishes are of special interest on account of the peculiar 
distortion of the eyes which these fishes exhibit. 

The eye muscles in the sole consist, as in symmetrical fishes, of four recti muscles 
and two oblique. The recti pass obliquely forwards from the back of the orbit to the 
outer surface of the eyeball, to which they are attached at equal distances ; in a 
symmetrical fish, as in every other vertebrate, one is attached at the dorsal side, one at 
the ventral, one to the anterior, and one to the posterior : these are respectively 
named the superior aud inferior, internal and external, recti. In the sole the superior 
rectus is uppermost in the natural position of the fish, having followed tlie torsion of 
the orbits without altering its position in relation to the iuterorbital processes of 
the frontal bones. Siinilarlj' the internal rectus of each eye is next to the interorbital 
septum. The superior and inferior recti of each eye are much thicker than tlie 
internal and external. All the recti of both eyes take their origin from the internal 
surface of the parasphenoid bone, within the cavity of the skull, but below the anterior 
part of the brain. 

Of the two oblique muscles of each eye that wliich is nearest to the interorbital 
septum is the superior, the other the inferior. Their direction is transverse to that of 
the recti muscles. The superior passes outside the end of the internal rectus, and is 
inserted into the eyeball between the insertion of that muscle and that of the superior 
rectus. The inferior oblique passes outside the end of the inferior rectus, and is 
inserted between the insertion of that muscle and that of tlie external rectus. The 
orio^ins of the oblique muscles in the sole and their direction are extremely peculiar and 
interesting. In a symmetrical fish the origins of these muscles are on the inner sides 
of the orbits, that is, on the side towards the median plane of the head. The median 
plane of the head in the sole is morphok)gically represented by the bony interorbital 
septum ; the oblifjue muscles of the ventral eye in the sole do arise from the interorbital 
septum, those of the dorsal or right eye do not. The superior oblique of the ventral 
eye arises from the small left ectethmoid which is on the right edge of the interorbital 
septum ; the inferior oblique arises from the external surface of the parasphenoid 
below the right ectethmoid. But both oblique muscles of the left or doi-sal eye arise 
from the inner surface of the left ectethmoid, which is not part of the interorbital 
septum. The origin of the muscles is just outside the olfactory foramen. The surface 
from which the muscles spring looks to the right side of the sole, or, in the natural 
position of the sole, directly upwards. Thus the direction of the oblique muscles of 
the dorsal (left) eye of the sole is at right angles to the direction of those of the ventral 
(richt). In fact, though the right ectethmoid bone has been shifted from its original 
position in the symmetrical fish to a very remarkable degree, the left ectethmoid is in 
the fame position: it has been rotated but not shifted in position. The surface of the 



51 

left ectetlimoid, to which the oblique eye mxiscles are attached, originally looked 
outwards to the left; now it looks upward, and it has become increased in size. 
Moreover, the left ectethnioid is still on the left side of the head, where it was 
originally before the distortion commenced. Another important fact is tliat the 
oblique muscles of ihe left eye are somewhat larger and stronger than those of the 
right. 

These facts seem to me to have an important bearing on the question of the evolution 
of the sole and other flat fishes, of the process by which the peculiar asymmetry which 
characterises them was produced. All zoologists are evolutionists now, and it is 
generally admitted that the flat fishes are descended from remote ancestors which 
were symmetrical throughout their Yives. This is sufficiently evident from the fact 
that all flat fishes when first hatched, and for some time afterwards, are at the 
present day perfectly symmetrical. But two entirely opposite views are at present 
held by different zoologists as to the process of evolution. One school of evolutionists 
goes beyond Darwin in one direction, the other in another. The former school believe 
that although the conditions of life and the habits of an individual animal do affect 
its structure, modify it in various ways, these modifications are never inherited and 
cannot therefore have anything to do with the process of evolution. All evolution 
according to this view is due to the natural selection of variations which are an 
advantage to the individuals in which they occur, and these variations are all due to 
causes existing before the development of the individual. Such variations are called 
congenital, and are inherited usually by the offspring of the ii'dividuals which 
possess them, and usually develop to a still greater degree in the offspring of two 
parents who both possessed them. These variations are entirely independent of 
the habits or conditions or the use and disuse of organs. Such evolutionists explain 
the distortion of the eyes in flat fishes in this way. A certain species of fish in remote 
ages found it necessary to lie on the bottom ; among the individuals of this species 
some had eyes which were very slightly asymmetrical, the lower eye being slightly 
nearer the edge of the body than in the other individuals. Consequently these 
individuals being able to see more than the others lived longest, escaped their 
enemies, and left most offspring. As they bred together, and as variations again 
occurred, some of these offspring had the lower eye still nearer to the edge of the 
head, and these survived while the others perished, and so on, until in course of long 
ages the present flat-fishes were produced. 

The other school of evolutionists believe that acquired characters are inherited to some 
degree. It is admitted that the use of an organ enlarges it and improves it. and they 
believe there is plenty of evidence tliat when the use of an organ in a particular manner 
is continued generation after generation the modification is partly inherited in eacli 
generation, and at last is wholly inherited. They hold therefore that tlie adaptations 
of ori:rans to particular purposes, which are so conspicuous in animals and in plants, 
are due to the use of the organs for those purposes, and, though the modification 

II 2 



52 

may be favoured and hastened by selection, it would take place without selection, 
while selection could not produce adaptations without the inheritance of acquired 
characters. They maintain, in fact, that there is no evidence of the occurrence of 
such variations as would give rise to adaptations except under the influence of 
stimuli and functional exercise. 

Thus these evolutionists would explain the distortion of the eyes in flat fishes in 
this way. A species of fish took to crouching flat on the ground on one side of the 
body. But at first they did not lie perfectly flat, but slanting, lifting up their heads 
so as to use the lower eye, and using the muscles of this eye so as to turn the pupil 
into a horizontal direction, and look along the edge of the head. In consequence of 
this, the lower eye pressed on the interorbital septum, and caused it to be flattened. 
This pressure being continued for millions of generations the flattening and distortion 
of the interorbital septum came to be inherited until at last the two eyes were on one 
side of the head. 

Now it is clear that no action of a given muscle of the eye could transport 
that muscle from one part of the head to another, and evolutionists who had not 
studied the anatomy of the head of flat fishes have made that objection to the above 
explanation. But no such transjjortation has occurred as was shown in the description 
given above. The attachment of the recti muscles of both eyes remains in the flat 
fish exactl}' where it is in the symmetrical fish. The cranial region aiid branchial 
rcjjion are unaltered. But the fishes which were the ancestors of the existing flat 
fishes, in order to twist the lower eye till its optical axis was almost parallel to the 
surface of the head, must have used the oblique muscles belonging to that eye. It is 
a physiological necessity that such a constant and extreme exertion of those muscles 
must in the individual have produced structural modifications, especially if it was 
commenced at an early age. The eye must have pressed on the interorbital septum 
in the sole oti the left side, and this pressure would not have been counteracted by 
any pressure on the other side, for the right eye was required to look upwards and 
ventrally. Such pressure must have caused absorption and distortion of the inter- 
orbital septum, that is to say, the septum would by that alone have become thin and 
flat and bent to the right side. The increased exercise of the left oblique muscles 
must also have caused them to become larger and stronger, and also have resulted in 
the enlargement of the bone to which they were attached ; for it is an established and 
certain fact that the exercise of a muscle causes it to increase in size and causes an 
increased development of bone at its attachment. But the direction of the strain of 
the muscles must have caused a torsion of the bone to which they were attached, 
so that the surface of attachment which originally looked outwards to the left came 
to look upwards. These are exactly the changes which we find to have taken place 
in the head of the sole. If the change had been due to the selection of variations 
which were independent of the eflects of function, then we should expect that the 
left ectethmoid would have remained symmetrical with the right, for the left eye could 



53 

have been worked in its present position just as well if tlie oblique muscles had been 
attached to the side of the interorbital septum, as the right muscles are. But, on the 
theory for which I contend, there must have been some fixed point or fulcrum which 
remained fixed while the action of the muscles altered the position of neighbouring 
parts in relation to this fixed structure. The left ectetmoid of the sole fulfils the 
precise conditions required of such a fulcrum. A man cannot lift himself up in a 
basket, and the eye muscles could not by physiological effects have removed themselves 
bodily by their own action to a new position. But two muscles by straining on their 
own attachment, when unresisted by other muscles could twist neighbouring structures 
round that attachment, must in fact do so, the bone to which they were attached 
remaining in the same position and becoming enlarged. This is exactly what we find 
to have taken place in the sole. Thus the change which has taken place in evolution 
in the eyes and orbits of the sole is exactly of the same kind and in the same direction 
as, but much greater in degree than, the change which must have taken place in the 
individual fish which lay on its side and looked out with its lower eye beyond the 
edge of its head. Why, then, should we hesitate to conclude that the evolution has 
been due to the accumulation, by inheritance, of the modifications due to known 
physiological effects of functional activity? The only reason for hesitation is that 
some zoologists say that acquired characters are not inherited, an assertion which 
.seems to me to be contrary to the evidence on the subject. However, this is not the 
place to enter upon a discussion of the question of the heredity of acquired characters. 
My purpose has been merely to describe the relations of the eye muscles to the orbits 
in the sole, relations which I believe are not accurately described in anj- existing 
anatomical treatise, and to point out that these relations are such as would necessarily 
have resulted if the distortion of the orbits and the migration of the left eye had been 
due in the course of evolution to the constant action of the oblique muscles of the 
left eye. It must be remembered that the other peculiarities in the structure of the 
sole, namely, the extension of the dorsal fin to the snout and the asymmetrical 
development of the jaws, are not in any sense consequences of the distortion of the 
orbits. In many flat fishes both eyes are on one side, as in the sole, while the jaws of 
the two sides are almost perfectly symmetrical, and the dorsal fin terminates behind 
the eyes. I believe that both these peculiarities in the sole are modifications due to 
physiological causes connected with the habit of lying on the left side; but it is certain, 
I think, that these physiological causes have nothing to do with the action of the 
oblique muscles of the left eye. In endeavouring to trace the evolution of the sole 
from a symmetrical ancestor each modification must be explained separatelj- ; the 
distortion of the eyes and orbits may be explained by the action of the oblique 
muscles of the eyes, but this cause does not in the least explain the absence of colour 
on the under side, nor the greater size of the jaws on the lower side, nor the anterior 
extension of the dorsal fin. 



54 



CHAPTEE TTT. 

THE YISCEEA, AXD VASCULAR SYSTE:\r. 

Tlie Viscera. 

In the female the body cavity consists of three parts: a main central cavity, and 
two extensions or diverticula opening out of it. The central cavity is situated 
immediately behind the gill region and beneath the ten anterior vertebrae, and extends 
back to the anterior ventral interspinous bone. The tvro diverticula extend backwards 
from the main cavity, one on each side of the median skeletal partition of the body 
along the ventral edge. These lateral cavities extend from a liltle behind the anus 
to yth the length of the body from the tail, getting narrower dorso-ventrally towards 
the posterior end. The median anterior cavitj' contains the stomach and part of the 
intestine, the liver, and the spleen {see Plate YIII, 1). The right lateral cavity is the 
larger, and contains four parallel sections of the alimentary canal, also the right ovary. 
The left cavity contains only the left ovary and a part of the left kidney, which projects 
imo it. 

The liver is shaped like a flat cake with one surface smooth and the other made 
irregular by the entrance of blood vessels, &c. The greater j)art of this smooth 
suiface is turned to the left, and occupies nearly the whole dorso-ventral extent of 
the main body cavity ; it is the oidy thing seen in that body cavity on removing the 
left body wall. But the liver is doubled on itself anteriorly so that a smaller portion 
of the smooth surface lies beneath the body wall of the right side in the anterior 
part of the body cavity. 

Projecting from beyond this surface towards the dorsal boundary of the body cavity 
on the right side is seen the gall bladder, which is spherical. The liver is attached to 
the anterior wall of the body cavity by a short ligament, situated in the median line 
towards the dorsal limit of the anterior wall, about 1 cm. long at its peritoneal 
attachment, and 3 mm. at its hei)atic. 

The oesophagus passes into the main body cavity at its dorso-anterior angle, dorsal 
to the liver, then with a very slight dilatation to form the stomach it passes baekwards 
enveloped between the two parts of the liver, then following the boundary of the 



II 



55 

main body cavity in the median plane the stomach curves downwards, endino- at 
the pylorus at the ventro-posterior angle of the body cavity. Then commences the 
intestine, the first part of which may, as usual, be called the duodenum. At its 
commencement this is but little narrower than the stomach, but it rapidly narrows, 
and, passing forwards to the antero-ventral angle of the body cavity, bends at an acute 
angle and runs backwards and upwards along the border of the right fold of the liver, 
crossing the stomach on the right side to enter the right lateral body cavity alonw the 
dorsal part of which it runs to a little distance from its posterior end. The duodenum, 
like the stomach, is white, and has thick muscular walls, but towards the posterior 
end of the right lateral cavity it commences to get thinner walled and wider, and also 
darker from the contents seen through the walls. It now bends completely on itself, 
becoming considerably wider, and so passes into what may be called the ileum, which has 
extremely thin walls. This passes forwards along the ventral side of the right cavity 
in contact ventrally with the right ovary till it reaches to about the middle of the 
main body cavity where, lying on the right side of the duodenum, it again bends on 
itself and passes into the next length, which may be called the colon. At the bend, 
and about a centimetre on either side of it, the walls are again white, thick, and 
muscular, and the diameter of the tube is much reduced at this portion, which forms 
a kind of ileo-colonic valve, but internally there are no transverse folds of the wall, 
only longitudinal folds. After the bend the tube again dilates, this time suddenly, 
and the colon, with thin flaccid walls, passes back again into the right lateral 
cavity dorsal to the ileum, to a point about 2 cm. anterior to the end of the 
duodenum. At this point the colon, without any change of character, passes into the 
rectum, which passes forwards again on the dorsal side of and partially covering 
the colon, to the antero-ventral angle of the main body cavity, wliei'e it opens at the 
anus. 

The spleen lies anterior to the stomach, between it and the liver, and a portion of it 
is sometimes visible on removing the right body wall, between the duodenum and the 
rectum. There is no pancreas, and no pyloric cteca. All the parts of the intestine 
and the liver and spleen are connected together by the branches of the splanchnic 
artery and portal vein : these are especially conspicuous between the duodenum and 
the liver, where they run from one to the other across the spleen. 

The gall duct runs downwards from the gall bladder and opens into the duodenum 
a little behind the pylorus on the anterior side. The hepatic duct leaves the liver iu 
the anofle between the two folds and joins the gall duct about 1 cm. from the gall 
bladder. 

Cutting through the CEsophagus and the terminal part of the rectum we now 
remove the whole of the intestine, liver, and spleen, and examine the kidne\-s auc? 
ovaries. 

The two ovaries extend, as has been said, along the ventral border of the right 
and left body cavities respectively. They are both about the same length, but the 



r^t 



5G 

ht is thicker. The ovaries are not suspended by membranes (mesoaria) as in 
symmetrical fishes, but lie like kidneys beneath the peritoneum which passes over 
them. Morphologically the mesoarium may be considered to have fused with the 
surface of tlie median i)artition which separates the lateral body cavities from one 
another. Or, to regard the evolution in a dillerent way, it may be that the ovaries 
have grow-n back post-anally beneath the peritoneum. Each ovary has a containing 
wall which is independent of the peritoneum, though attached to it : the latter can be 
separated from the former with facility. The ovarian artery and vein pass down together 
on each side from the posterior end of the main body cavity, and run along the dorsal 
side of each ovary. The walls of the two ovaries unite anteriorly on the ventral side 
of the main body cavity to form a single wide tube whic-h opens to the exterior behind 
the anus and conducts the ova to the exterior, ^\■ll^■u tlie o\;uy is cut open tlie 
nerminal surface covered with projecting ovigerous lamellae having a gejieral 
lontritudinal direction, is seen to extend all round the internal surface except along 
the median ventral line, where the surface of the ovarian wall is quite smooth and 
destitute of ovigerous lamellte : this probably represents the suture along which in 
development the edges of the ovarian lamina joined together to form a tube. 

On the dorsal wall of the main body cavity the renal organs form abroad reddish band, 
placed in the centre and symmetrically, the two kidneys seem to be fused together in 
the middle line. No part of the renal mass is continued into the right lateral body 
cavity, but it is continued as a bulging thick mass into the dorsal part of the left 
lateral cavity, where it is in contact ventrally with the left ovary. From the ventral 
anterior corner of tliis mass there comes off a single short renal duct which opens out 
into a large urinaiy vesicle. This vesicle sends a prolongation backwards between 
the left ovary and tlie wall of the left lateral cavity, and it extends do^^^lwards behind 
the common oviduct, between this and the wall of the main body cavity, to open to 
the exterior on a small papilla on the right side. The opening of the oviduct, 
although in the same depression of the skin as the anus, is separated from the 
latter by a fold of membrane. Anteriorly the kidneys extend hivond the main body 
cavity between the oesophagus and the muscles dorsal to it, as far as the posterior 
surface of the skull. 



Description of tlie Viscera of the male from a specimen Ifoot long (SI cm.). 

Plate IX. 

The intestines are arranged as in the female except that they do not reach quite so 
far back in the right lateral body cavity, that is, they are slightly shorter. In front 
of the bend which divides the colon from the ileum, is seen the urinary bladder, 
distended. No part of the testes is seen without disturbing the organs in the body 



57 

cavity. Wlien the intestines are lifted up or removed, tlie riglit testis is seen, a 
triangular flat solid mass about 8 mm. broad at its posterior end, and 1 3 mm. long, 
lying at the anterior end of the right lateral body cavity, close to the front edge of tlie 
skeletal partition to which its inner surface is attached. 

On the left side there is no left lateral body cavity, but the posterior portion of the 
fused renal organs extends backwards between the lateral muscle and the skeletal 
partition : this part of the kidney is as large in proportion as in the female, and has the 
same relations to the urinary bladder. 

The left testis is only about half the size of the right. In this specimen it was 4 mm. 
troad above, and 10 mm. in length. The right testis is somewhat flat, and its greatest 
length is nearly antero-posterior in direction ; the left has the form of a triangular 
pyramid with its point downwards, and its greatest length is dorso-ventral in direction. 
The left testis is situated in the main body cavity attached to the peritoneum over the 
surface of the kidney by a membrane, the mesorchium. 

From the apex of each testis passes off the vas deferens or duct by which the milt 
or semen is conveyed to the exterior. Each vas deferens contains not a single cavity 
but several, and it is attached to the anterior surface of the urinary bladder. The 
vasa deferentia being translucent are not conspicuous ; their external aperture is at 
the end of a small papilla on the right side, which is pierced also by the terminal 
part of the urinary duct. Thus in both sexes there is a papilla on the right side ; in 
the female it is a urinary papilla, in the male it is urinogenital. In the figure the 
wooden rod is inserted through the anus into the end of the rectum, while the black 
bristle passes into the urinary bladder the walls of which are exceedingly transparent 
and indistinct, especially when the bladder is empty and collapsed. 

Thus the male organs of reproduction in the sole are extraordinarily small in 
proportion to the size of the body. In other flat fishes, e.g., the plaice, PL platessa, or 
merry -sole, Fl. microcephalus, they are smaller than the ovaries, it is true, but many 
times larger than those of the sole, and in the breeding season they become enlarged 
and soft, and of a milk-white colour. In this condition they at once attract notice 
when a male fish is cut open. In the sole, on the contrary, although the testes become 
slightly enlarged during the spawning period, they become neither white, nor soft, 
nor conspicuous. In fact they are not known to the fisliermen, who are unable to 
recognise in the siuall yellow organs of the sole the male reproductive organs 
which they usually find in other fishes as large, white, soft, and conspicuous 
masses. The testes of the sole are, moreover, completely concealed beneath the 
intestine. Until recently even ichthyologists were for the most part unacquainted 
with the structure and relations of the male organs of the sole. In the 
Fifth Annual Eeport of the Fishery Board for Scotland, p. 233, it is stated that " the 
hatching of the sole, e.g., presents this one great difficulty, that males are rarely ever 
captured, or, at least if captured, are seldom identified." As a matter of fact males 



58 

are captured in greater numbers than females, but fishermen are unable to distinguish 
the males from unripe or immature females. 

One part of the viscera, which has the same relations in both sexes, still remains 
undescribed, namely, the anterior part of the intestine, and the gills which are con- 
nected with it. The anterior part of the intestine itself needs no very elaborate 
description : it consists simply of the mouth and throat, the walls of which differ oidy 
from the stomach in the fact that they are almost everywhere continuous with the 
surrounding muscles and otlier tissues, instead of being separated from them by part 
of the body cavity. Beneath the throat there is a part of the body cavity entirely 
separated from the rest, namely, the pericardium, whicli contains the heart, and wliich 
will be described below. Tlie teeth previously mentioned as connected with or 
embedded in tlie superior and inferior pharyngeal bones of course project through the 
walls of the throat, and help to masticate or grasp the food. The series of basihyal 
and basibranchial bones, clothed with raucous membrane, form a pointed conical tongue 
in tlie floor of the mouth, which is used in swallowing. 

At the sides of the throat is the important respiratory apparatus. Between the 
branchial arches are a number of clefts by which the cavity of the throat opens to 
the exterior. The bony arch is clothed with connective tissue, muscle, and mucous 
membrane, and this mucous membrane becomes continuous through the cleft with the 
outermost layer of the skin on the external surface of the body. The most anterior 
cleft is between the hyomandibular bone and the iirst branchial arch : the cleft extends 
upwards to the middle of the epibranchial bone, downwards to the end of the cerato- 
branchial. The 2nd, 3rd, and 4tli clefts become gradually shorter, scarcely extending 
upwards beyond tlie cerato-brauchials. The 5th cleft is very short, it is situated 
between the 4th cerato -branchial bone and the 5th cerato-branchial or lower pharyn- 
geal bone. The latter is continuously connected by muscle and connective tissue with 
the pectoral arch ; there is no cleft behind it. On the outer face of each arch there is 
a double series of long straight filaments, the branchial filaments. Each of these is 
supported by a rod of fibnnis skeletal tissue which runs up its centre, and between 
this rod and the epithelium, or layer of delicate cells which covers the surface of the 
filament, there is a ricli plexus of capillary blood vessels. The blood coursing through 
these gives out its carbonic acid to the sea water which passes through the gill clefts 
and absorbs oxygen from the sea water, which oxygen is necessary for the oxidization 
of the tissues that goes on throughout life. 

In front of the first branchial cleft, running in an antero-posterior direction beneath 
the dorsal part of the hyomandibular bone, is a rudimentary branchia, composed not 
of long branchial filaments, but a few vascular folds of the mucous membrane : this 
is called the pseudo-branchia and is found in the majority of bony fishes. The pseudo- 
branchia represents part of tlie brancliia of the hyoid arch. On tlie inner surface of 
the branchial arclies there are ?mall fleshy projections; in many fish these are long 
projecting rods called the gill rakers. In the sole they are rudimentary. 



59 

The brancliiostegal rays support a membrane which is externally for the greater part 
of its length contiiujous with the opercular flap, but is free at its edge, and extends 
somewhat beyond the flap ; it forms a concavity which directs the water pressed out 
in expiration upwards towards the base of the pectoral fin. The edge of the branclii- 
ostegal membrane is, in ordinary respiration, kept pressed figainst the posterior wall 
of the branchial cavity except opposite the base of the pectoral fin, where the membrane 
forms a small aperture by which the water that has passed over the gills escapes. The 
opercular flap supported by the opercular bones forms the external wall of the 
branchial chamber, in which the branchise are contained and concealed, but the oper- 
cular flap is morphologically nothing but a fold of skin projecting backwards from the 
hyoid arch and supported by dermal bones. The branchiostegal rays represent the 
branchial skeletal rods of the lower part of the hyoid arch : they have been much 
enlarged, and the filaments they supported have lost their branchial function, and 
coalesced to form the branchiostegal membrane. 



Minute Structure of the Reproductive Organs and Development of the Reproductive 

Elements. 

It has already been mentioned that the ovary consists of a hollow tube from the inner 
surface of the walls of which 23roject a number of longitudinal lamellas containing the 
ova. A section of a j'oung ovary of the right side is represented in PL XIII, 1 , as 
seen under a low magnifying power, namely Zeiss' objective A, ocular 2, The specimen 
from which this ovary was taken was 7j in. long, and was immature. But the 
structure of a mature ovary is similar in all respects except the size of the ova. 
The wall of the ovary consists of laminated fibrous tissue, and the ovigerous lamellaj 
are supported by projections of this tissue into the interior of the ovary. On the 
dorsal side of the transverse section are seen two blood vessels, the ovarian arterj^ and 
vein. Tlie ovigerous lameUas are absent from a small portion of the ventral wall of 
the ovary, where the internal surface of the wall is smooth and barren. The surface 
of the ovigerous lamellas is covered by a thin epithelium of cells too minute to be 
distin<mished separately under a low power. Here and there in this epithelium young 
ova are seen developing. The epithelium is called the germinal epithelium, and 
from its cells all the ova are originally derived. The older ova are seen below the 
epithelium in the substance of the ovigerous lamelliB. The lamellae contain in tlieir 
centre a plate of somewhat dense fibrous tissue, from which a loose reticulum of 
fibrous strands and bands extends to the germinal epithelium. The older ova sink 
into this loose fibrous layer, and each ovum is surrounded and enveloped by strand.s 
of the fibrous tissue. The spaces in the fibrous reticulum are doubtless in life filled 
with lymph, while the tissue itself is richly supplied with capillary blood vessels. The 

I 2 



GO 

largest ova in the ovary at this stage are still verj' young, and each consists of a 
protoplasmic mass containing a nucleus. The nucleus is a spherical vesicle bounded 
by a membrane and containing protoplasmic strands and a number of nucleoli 
which are all situated at the periphery of the nucleus. In a stained preparation the 
nucleoli and the protoplasm of the ovum surrounding the nucleus are deeply stained, 
but the rest of the nucleus, consisting chiefly of liquid contents, is scarcely stained at 
all. Thus in each ovum the nucleus is seen as a clear central space containing several 
deeply stained globules arranged within its external border. There is little doubt 
that the fibrous connective tissue in the living state is more compact than I have 
represented it to be. The ova contract in the process of preparation and leave open 
spaces between them across which fibres are seen passing. But nevertheless it is 
certain that the fibrous tissue is reticular, and that it is traversed bj* spaces containing 
lympli. 

When a portion of an ovigerous lamella from a young ovary is examined with a 
high power it presents the appearance shown in PI. XIII, 2. The preparation from 
which this figure is taken was made from the ovary of a sole 10^ inches long, killed 
in January. This also was an ovary which had never produced ripe ova, an im- 
mature ovary. It will be seen that the cells of the germinal epithelium are extremely 
minute and their outlines undefined. The ova are evidently produced by the 
enlargement of single cells of this epithelium, and as they increase in size they pass 
downwards into the fibrous "stroma." Even round the largest ova in an ovary at 
this stage no envelope can be detected except a fibrous membrane belonging to the 
"stroma" of the ovary. The protoplasm of the ovum, although it has grown in 
quantity, still exhibits no differentiation. The largest ovum represented in Fig. 2 is 
•12 mm. in diameter. 

But ova which are approaching maturity show a much more complicated structure. 
Fig. 3 is drawn from a section prepared from an ovary in the spawning condition ; 
in fact the ovary was almost spent, but a few immature ova remained in it, and a 
section of one of these is represented in the figure. This ovum is seen to be enclosed 
by a thick envelope, exhibiting in section close set radiating lines. This envelope is 
not stained in the preparation. The radiating lines are really exceedingly fine tubules 
passing through the substance of the envelope and through these the protoplasm of the 
ovum communicates with the nutritive fluids outside. This envelope is the innnature 
stage of the membrane surrounding the ripe ovum when it is shed, but at this stage it 
is much thicker in proportion to the size of the ovum than in the state of maturity. 
This envelope may be called the vitelline membrane ; in the eggs of some fishes it is 
differentiated into two layers, but in the sole I can find no distinction except that the 
exterior surface of the membrane forms a kind of thin cuticle. The ovum within the 
membrane presents an appearance very different from that of tlie j-ounger ovum 
previously described. Instead of a mass of granular protoplasm there are here a great 
number of spherical vesicles crowded together. These vesicles contain a number of 



61 

granules scattered through a transparent substance. They are the yolk vesicles. 
Attentive examination shows that the yolk vesicles are contained in the original 
protoplasm of the ovum, which everywhere extends among them, forming a network. 
In fact the yolk vesicles are developed by the protoplasm within itself. The protoplasm 
takes up the nutritive liquid materials derived from the blood and alters these by its 
living chemistry so as to form these yolk vesicles which grow as it were at all points 
throughout the substance of the protoplasm. Tu the mature ovum these yolk vesicles 
become homogeneous and transparent, and flow together, with the exception of a few 
of them, which remain separate but transparent near the outer surface of the ovum. 
In the ovum now under consideration the nucleus retains the structure described in 
the younger stage, and is still near the centre of the ovum. When the yolk vesicles 
fuse the nucleus passes to the exterior with the protoplasm, the whole of which forms 
a superficial layer enclosing the central semifluid yolk as in a blalder. 

We have now to consider the ovarian structures surrounding the egg at the stao-e 
represented in Fig. 3. It is easy to recognise outside of all the thin membrane of 
fibrous tissue connected with and belonging to the stroma of the ovary. This may be 
called the follicular membrane, the ovarian capsule enclosing the ovum being usually 
known as the follicle. The follicular membrane exhibits nuclei along the course of the 
fibres composing it, and it contains a number of capillary blood vessels, communicating 
with larger vessels in the stroma (b.v. in Fig. 3). But within the follicular membrane 
is a regular epithelium which was not seen in the younger stage of the ovum. This is 
composed of a single layer of cells possessing large distinct nuclei. These cells in the 
preparation are separated from one another at their internal ends, but this is probably 
due to the contraction caused by reagents. Such a follicular epithelium is found round 
the ripening ova of all vertebrates. But it is still an open question whence it is 
derived. It has been maintained by many great authorities that the follicular cells 
are derived from the germinal epithelium ; that when on ovum separates from the 
epithelium and sinks into the stroma it takes with it a few other cells of the epithelium, 
Avhicli multiply by division and form the foUicular epithelium. This conclusion 
has been drawn mainly from the study of the ovary in embryos, not from that of 
developing ova in adult animals. As I have shown I have failed to trace any 
connection between the follicular epithelium and the germinal epithelium. The former 
seems to me to be entirely wanting for a considerable period after the young ovum has 
separated from the germinal epithelium. The cells of the follicular epithelium become 
visible about the same time as the commencement of the vitelline membrane. If these 
cells are not derived from the germinal epithelium they must be derived either from 
the egg itself or from the stroma of the ovary. There is no evidence of their derivation 
from the egg itself at least in bony fishes, and it is inconsistent with what we know of 
fibrous tissue to suppose that the nucleated fibres can produce cubical cells. The 
follicular cells cannot be developed independently from nutritive material derived from 
the blood, they must be descendants of previously existing cells, for we know of no 



62 

case in which nucleated cells arise, except as the progeny of other cells. Tliere is 
thus only one source left to which we can attribute the origin of the follicular cells, 
namely, the colourless aniccboid wandering lymph cells, which occur in the interstitial 
l}nnph spaces of all connective tissue. These cells are usually small, and it is possible 
that they might intrude themselves through the spaces between the fibres of the 
follicular mem])rane and so take up a position between that membrane and the surface 
of the vitelline meiubrane, and then growing in size form the follicular epithelium. 
The question of the origin of the follicular cells cannot however be considered as 
decided ; Professor Emery in his nionograph on Fierasfer, like myself, considers it 
improbable that they are derived from the germinal epithelium, but expresses no 
positive opinion as to their real origin. 

As the egg in the ovary increases in size and approaches maturity its circumference 
reaches again the surface of the ovigerous lamella, and ultimately when it is quite ripe 
the germinal epithelium, the follicular membrane, and the follicular epithelium burst and 
the ripe egg enveloped only by the vitelline membrane escapes into the cavity of the 
ovary, whence it passes out through the external genital aperture to the exterior, >vhere 
it is fertilised. 

The structure of the testis of the sole is very different from that of the ov^ry, and 
closely resembles that of the testis in other bony fishes. PI. XIII, 4, shows the structure 
of the testis of a young male sole 9 in. long, killed February 4lh, 1889. The testis of 
a full-grown male sole is similar, but I have represented the transverse section of 
a small testis in order to include the whole of the section without making the 
figure inconveniently large. The substance of the organ consists principally of 
cylindrical tubes having walls of fibrous membrane and containing the spermatic cells. 
These tubes are closed at the end which is most remote from the testicular duct leadins 
to the exterior, and these closed ends are all situated immediately beneath the surface 
of the organ. From the closed ends the tubes pass radialh^ inwards towards the 
central region of the organ, except at the sides where their course is more longitudinal. 
The tubes are sp numerous as to be in contact with one another along their sides. As 
in the case of the ovary the " stroma " of the organ consists qf fibrous connective tissue 
which fills up the interstices between the testicular tubes and forms a thin layer rouiul 
the organ externally. In the central region of the organ the testicular tubes 
conmuinicate with a number of longitudinal tubes much smaller in number than the 
tubes themselves and of various sizes, some smaller, some larger, than the testicular 
tubes. These longitudinal tubes convey the si)ermatozoa towards the efferent ducts, 
and do not themselves produce spermatic cells : they are scattered with no regular 
arrangement through the dense fibrous stroma. Infcriorly the fibrous stroma of the 
testis is looser in texture and becomes contiiuious with the fibrous connective tissue of 
the wall of the body cavity to M'hich the testis is attached. Thus, to use the terms 
frequently employed in liuinan anatomy, the testis of the sole consists of a corlicid 
portion and a central medulla, tlie cortical portion consisting of tubes placed 



perpendicular to the surface, tlieir outer ends being closed, and the medulla of 
longitudiual tubes separated from one another by fibrous connective tissue. This 
medullary portion is prolonged beyond the organ itself in the form of a band which 
passes down the surface of the urinary bladder to the genital opening. Sections of 
this baud show that the longitudinal efferent tubes do not unite into a single duct or 
vas deferens, but are only slightly reduced in number by coalescence, so that a large 
number of tubes remain separate even to the external opening. Fig. 6 exhibits a 
section of the cord or band connecting the testis with the exterior and containino- the 
separate efierent tubes. This section is more highly magnified than that shown in 
Fig. 4, and is taken from the testis of a full-grown male preserved while in full genera- 
tive activity, in March, 1889. The spermatozoa are seen within the efferent tubes, 
completely filling the cavity of some of them, and appearing under a low magnifyin<^ 
power as deeply stained granules : these granules are the heads of the spermatozoa, 
the tails or vibratile appendages not being visible. 

If the cortical tubes in the section shown in Fig. 4 are examined under a more 
powerful objective, each of them presents the structure shown in Fig. 5. At the closed 
end of the tube are a number of large polygonal cells forming an epithelium. Each 
of these cells has a large nucleus with many nucleoli ; lower down the tube is filled 
with smaller and smaller cells produced by the division of the large cells. The large 
cells are evidently constantly being multiplied by division, and after reaching a certain 
size each is pushed down into the cavity of the tube where it divides and subdivides, 
forming a cluster of smaller cells. In some parts of the tube such clusters of small cells 
produced from a single original cell can be distinguished, but they easily break up and 
the cells of various clusters are confused together. In some of the voung clusters 
near the closed end of the tube all the nuclei are seen in a state of division showing 
that each cell is dividino; into two. 

The large cells at the closed end of the tube correspond to the germinal epithelium 
of the ovary ; they do not extend down the sides of the tube, but are confined to its 
end : they are the male germinal cells and from them all the spermatozoa are 
produced. 

As the cells pass down the testicular tube they get smaller and smaller, and in the 
lower ends and in sections of the deeper portions cut transversely they are seen to have 
reached their limit of subdivision, for amongst them are seen deeply stained minute 
spherical bodies which are the heads of spermatozoa. The minute cells produced 
by continued subdivision are converted into spermatozoa and are called the 
spermatoblasts. The details of the development of a spermatozoon from one of 
these spermatoblasts can only be followed out by teasing up a portion of the testis on 
a glass slide and examining it microscopically with the aid of reagents. The process 
cannot be followed satisfactorily in sections because in these the elements are cut uj) 
into pieces. I have not followed the process of development in the sole ; I will 
therefore merely explain here that the protoplasm of the spermatoblast elongates 



G4 

into a slender filament, while the nucleus alters in properties, imbibing stains such as 
carmine more intensely, and forms what is called the head of the spermatozoon. 
During the spawning period all the testicular cells, except the large cells of the 
male germinal epithelium at the closed ends of the testicular tubes, are converted into 
spermatozoa, which are conveyed to the exterior suspended in a litpiid similar to 
lymph. Tliis li(piid is ])roduced within the testis, being probably exuded from 
the blood vessels and lymph of the testicular stroma into the testicular tubes. The 
liquid containing the spermatozoa is usually called the milt. When the spermatozoa 
reach the sea water they swim about actively, and when one meets a ripe ovum it 
enters its substance and fertilises it. 



The Vascular System. 

The blood vessels ramify through all the tissues, including the skin and nervous 
system, which have not yet been particularly described. Ihit as the heart, which is the 
central organ of the vascular system, is closely related to the body cavity and to the 
branchiae, the system may be conveniently described here. 

The heart, as was before mentioned, is enclosed in a special chamber of its own, 
which is really a part of the body cavity, though it is entirely shut off from the visceral 
cavity in which the organs of digestion, &c., are contained. This cavity containing the 
heart, the pericardium, is situated between the posterior and internal walls of the two 
branchial chambers ; the cavity is wedge-shaped, the edge of the wedge being anterior, 
the base posterior. Posteriorly the pericardium is separated from the visceral 
cavity by a thin membrane which lies in front of the liver and below the gullet or 
oesphagus. Outside the pericardium on either side is the boiie called the clavicle. 
The heart itself is conical in shape, the point being ventral and directed downwards 
and slightly forwards, the broad base being dorsal. It is hollow and divided into two 
portions connected by a valve. The dorsal portion has very thin walls, and is called 
the auricle ; the ventral portion has thick muscular walls, and is called the ventricle. 
Into the dorsal end of the auricle open three large veins by which the blood which has 
passed through the various parts of the body is conducted into the cavity of the 
auricle. These veins are the Juctus Cuvieri which pass one on either side of the 
oesophagus from the kidneys, and the hepatic vein which passes forwards from the liver 
below the oesophagus. The ductus Cuvieri of each side is formed by the union of two 
veins, one ruiuiing forwards in the substance of the kidney and conveying the blood 
from the trunk, the other running backwards from the head and conveying the blood 
from the brain, skull, &c. ; these are called the anterior and posterior cardinal 
veins. 

The ventricle sends off a single main l)lood vessel, the ventral aorta. At the opening 
of this vessel from the ventricle, there are three internal folds or valves which prevent 



G5 

the blood returning to the ventricle. This vessel passes forwards along the dorsal 
edge of the jugular bone, and beneath the basi-branchials it divides, giving off on each 
side an artery to each of the first four branchial arches ; from the artery of the first 
arch a branch passes to the pseudobranchia. The fifth arch, bearing no branchial 
filament, does not receive a special branchial artery. The branchial arteries run along 
the branchial arches giving off smaller vessels which break up into the capillaries of 
the branchial filaments. These capillaries unite again into the efferent branchial 
vessels which run in the branchial arches towards the dorsal side of the pharynx or 
throat, where they unite together into a single median dorsal aorta. From the efferent 
branchial vessels are given off arteries which supply the brain, skull, and other parts 
of the head. From tlie dorsal aorta is given off at the anterior end of the body cavity 
the coeliac artery which supplies the intestine spleen, and liver with arterial blood. 
The dorsal aorta runs backwards in the canal formed by the series of divergent bases 
of the ventral spines of the vertebrae, and is therefore in its anterior part dorsal to the 
kidneys. It gives off special arteries which descend to supply the generative organs. 
It also throughout its course gives off a pair of arteries to each segment of the lateral 
muscles, fi-om which branches supply the skin, bones, and all parts of the body. 

The return of the exhausted venous blood from the tissues to the heart takes place 
by a somewhat curious route. The veins of the head unite into the two anterior 
cardinals, already mentioned, one on each side. But nearly all the veins of the trunk 
fall ultimately into the caudal vein which runs forwards in- the same bone-protected 
canal as the aorta, as far as the interval between the ventral spines of the ninth and 
tenth vertebra3, where it bends suddenly towards the ventral edge of the body and 
enters the dorsal side of the renal mass. The veins of the trunk in front of the caudal 
vein fall into the kidney by separate collecting veins. A number of the veins of the 
ventral side of the trunk, behind the kidney, unite into a longitudinal vein, which runs 
forwards along the left side of the median skeletal partition and enters the posterior 
apex of the part of the kidney which extends backwards on the left side behind tlie 
main body cavity. Thus nearly aU the venous blood in the trunk is conveyed into the 
renal mass, where the urinary excretion is extracted from it, and whence it is passed 
on by the posterior cardinal veins to the heart. The veins of the spleen and intestines on 
the other hand unite into a single vein which enters the liver where it breaks up into 
capillaries, and these unite again to form the hepatic vein which opens into the auricle. 



K 



GG 



CHAPTER TV. 
THE NERVOUS SYSTEil 

The Brain. — Tlie brain of the sole has no veiy special features which distinguish it 
among those of other bony fishes. The position of the brain is almost entirely 
unafTected by the change which has taken place in the normal jx>sition of the fish ; the 
posterior part of the skull, as was previously pointed out, has neither twisted nor 
become asymmetrical, and the corresponding part of the brain also retains its original 
position and symmetry. But it seems still more remarkable that the anterior part of the 
brain has not to any great degree followed the anterior part of the skull in the rotation 
which the latter has performed. When the brain is exposed from the upper (right) 
side of the fish, the right side of the organ is seen, the extreme anterior end being 
alone very slightly turned round towards this side. This absence of change in the 
position of the brain is not so paradoxical when we compare carefully the relation of 
the organ to the skull. The anterior end of the biain lies beneath the posterior 
portions of the frontal bones, and these retain their original position. 

It might have been expected that the change in the position of the anterior cranial 
nerves would have caused a greater twisting of the brain ; but we find that the trunks 
of the nerves have moved while their roots have been very slightly affected. 

Viewed from the dorsal side the brain exhibits the same series of ganglionic masses 
which are seen in other bony fishes. At the posterior end is the single median globular 
cerebellum which projects backwards above the anterior thickened continuation of the 
spinal cord, called the medulla oblongata. In front of the cerebellum is the pair of 
masses whence the optic nerves arise, the optic lobes, each of which is almost as large 
as the cerebellum ; in front of thesa again is the pair of cerebral hemispheres which 
are slightly smaller than the optic lobes, and immediately in front of the cerebral 
hemispheres are the olfactory lobes. In some bony fishes the olfactory lobes are 
removed to some distance from the brain and placed in proximitj- to the olfactory 
capsules, being connected with the brain by long nervous peduncles or crura ; e.g., in 
the cod and carp. But in the sole as in other flat-fishes, and in the perch, mackerel, 
pike, gurnard, and others, the olfactory lobes form part of the brain and are at a 
distance from the olfactory capsules ; witli which they are connected by the olfactory 
nerves. 



67 

The under surface of tlie brain exhibits beneath the cerebellum the continuation 
forwards of the medulla oblongata which forms as it were the stalk supporting the 
dorsal lobes. Beneath the front part of the optic lobes, however, an inferior outgrowth 
is seen ; this consists of a pair of lobes called the lolji inferiores between which is a 
vascular organ called the pituitary body, or hypophysis cerebri, supported on a hollow 
conical outgrowth called the iufundihulum. 

The brain contains a central cavity which is the continuation of the central canal of 
the spinal cord. This cavity terminates in the middle line between the cerebral 
hemispheres, but laterally it sends off two diverging prolongations into the interior of 
these hemispheres. The medulla oblongata and its continuation, the crura cerebri, are 
situated below the ceiitral cavitj', while the cerebellum, the optic lobes, and the upper 
part of the cerebral lobes are enlargements of the roof of the cavitj^ The infundibulum 
and pituitary body form a downward diverticulum of the cavity beneath the point 
where it bifurcates into the cavities of the cerebral lobes ; and a corresponding diver- 
ticulum towards the dorsal side exists between the anterior part of the optic lobes, and 
is called the pineal gland. The pineal gland, like the pituitary body, is a vascular 
structure in fishes. In some reptiles it has been found to have a structure resembling 
that of the vertebrate eye. 

The olfactory lobes are continuous with the inferior portion of the cerebral hemi- 
spheres. In the sole the left olfactory lobe is somewhat larger than the right, a dillerence 
which is related to the great development of the left olfactory capsule. But there is no 
inequality in the size of the optic lobes or optic nerves, such as that which according 
to Owen occurs in the halibut and some other Pleuronectidce. In Owen's figure of 
the halibut the right optic lobe and left optic nerve are the larger ; the eyes of this 
species, as of the sole, are on the right side, so that the larger structures are those 
belonging to the eye which has migrated. 

It would naturally be inferred that the left eye was larger than the right in the 
halibut, but I have not been able to find any allusion to an iricquality in the size of the 
eyes themselves. 

As in all bony fishes the brain of the sole is much smaller than the cavity in which 
it lies. The widest part of the cavity within the skull is the posterior part : here the 
brain passes forwards from i\i.e foramen magnum as an axis in the centre of the cavity, 
the surrounding space being occupied by the auditory organs. The sacculi meeting 
in the middle line below, occupy the space below the brain, while the semicircular 
canals intervene between the latter and the skull-walls dorsally and laterally. A 
transverse ridge on the inner surface of the skull-wall, forming part of the sphenotic 
and prootic bones, limits anteriorly the cavity occupied by the saccuU. In front of 
this ridge is another ventral depression occupied by the optic thalami and pituitary 
body, while aljove the optic loljes and cerebral hemispheres there is a considerable 
soace occupied only by spongy connective tissue containing fluid— tlie arachnoid 
membrane. The internal hollow of the parasphenoid bone in front of the pituitary 

K 1 



68 

body is occupied by the insertion of the muscles of the two eyes, these muscles bein<T 
separated from the interior cavity of the skull by a tough membrane, continuous with 
the dura mater posteriorly, and anteriorly with the membrane which completes the 
septum between the orbits. This membrane is pierced for the exit of the optic, 
olfactory, and other nerves, and on it rest the olfactory lobes. 



The Cranial Nerves. 

The olfactory nerves pass from the olfactory lobes to the olfactory capsules, termi- 
nating in the olfactory epithelium of these organs. Owing to the rotation of the left 
eye and orbit the position of these nerves in the sole is peculiar. Each olfactory nerve 
in all fishes passes over the dorsal side of the recti muscles of the eye. Tlie relations 
of the nerves to surrounding structures are not altered in the sole, but the rotation of 
the eyes has brought the olfactory nerves into asymmetrical positions. Thus both of 
these nerves are apparently on the upper (right) side of the head, though morphologi- 
cally they are on opposite sides. Both of them, like other structures connected with 
the orbits, are on the coloured side of the head, to the right of the anterior part of the 
dorsal fin. The left nerve passes above the recti muscles of the left eye close to the 
interorbital septum, and in front of these muscles bends downwards and passes through 
the large foramen in the left ectethmoid bone (PI. XI, G, I) to reach the left olfactory 
capsule on the lower side of the head. 

The right nerve has a perfectly straight course along the ventral (right) siile of the 
interorbital septum, dorsal to the recti muscles of the ventral (right) eye. It passes 
through the foramen in the right ectethmoid without any bending, and then bends 
slightly downwards to the olfactory capsule of the upper (right) side. 

Each of these nerves, though spoken of in the singular, consists of a bundle of 
separate nerves, whieli are separate tliroughotit their course, and not united into a 
single cord. 

The optic nerves, as usual in bony fishes, cross one another at their origin without 
mingling. The dorsal (left) nerve is very slightly longer than the ventral (right). The 
left arises from tlie lower side of the right optic lobe in front of the lobiis inferior or 
optic thalanms, the right from a corresponding position on the left side. The optic 
nerve passes between the internal and superior 7-ecins close to their origin into the 
space enclosed by the recti muscles, and so reaches the eye-ball. 

The third, fourth, and sixth pairs of cranial nerves are motor nerves all distributed to 
the nmscles of the eyes. The third pair are called the motores oculorum and split up 
into branches which enter ths superior, inferior, and internal recti, and the inferior 
oblique nmscles. The fourth pair of nerves are called trochleares and supply the 
superior obliciue muscles exclusively. The sixth pair are called nbduccntes, and enter 
only the external recti maicles. These nerves arise from the sides of the lower part of 



\ 



no 

the brain behind tlie origins of the optic nerves, and pass from the slvull 1)y apertures 
in the membrane wliich closes its anterior opening. 

The fifth nerve or trigeminal arises by several roots from the side of the medulla 
oblongata below the cerebellum : in its origin it is closely connected with the seventh 
or facial nerve. In fact the two nerves arise from a number of roots common to both, 
of which the dorsal are sensory, the ventral motor ; the fifth nerve is chiefly composed 
of fibres from the sensory roots, with the addition of some from the motor, while the 
facial consists chiefly of fibres from the motor roots, with the addition of some iiom 
the sensorj'. 

The fifth nerve consists of a large number of branches. It does not leave the skull 
by a single trunk, but divides on the inner wall of the skull into several, the largest 
and most important of which leaves the skull after a very short course by the large 
trigeminal foramen in the lower part of the sphenotic bone. The other two branches 
run for some distance on the inner wall of the skull before emerging ; one of them runs 
directly forwards and emerges through the anterior membrane wliich separates the 
skull from the orbits ; this forms the orbito-nasal nerve ; the other curves upwards arid 
forwards and emerges by a small foramen in the frontal bone. As the corresponding 
nerves difier on the two sides it will be necessary to describe them separately. 

The course of both orbito-nasal nerves, like that of the two olfactory, is to be followed 
by dissection of the upper side of the head ; for each orbito-nasal nerve lies in close 
relation to the olfactory, lying in the ordinary fish dorsal to the olfactory and between 
the eye muscles and the interorbital septum. Accordingly in the sole the orbito-nasal 
nerves are found on the upper side of the head, one on either side of the interorbital 
septum. But the dorsal (left) is much larger, and longer than the ventral (right). The 
left nerve passes over the surface of the mesethmoid bone at the bottom of the rounded 
notch between the left ectethmoid and the mesethmoid, and then enters the gelatinous 
tissue of the end of the snout, sends branches to the skin of the upper side at this part 
of the snout, but is chiefly distributed to the tactile filaments of the skin on the lower 
side between the olfactory capsule and the edge of the snout. The right nerve just 
behind the right ectethmoid passes into a canal between the right frontal bone and the 
right ectethmoid, and thence emerges again on the right upper surface of the meseth- 
moid, enters the gelatinous tissue of the snout, and supplies the small area of skin on 
the upper side between the mouth and the apex of the snout. 

The right dorsal branch of the fifth, after its upward course on the internal surface 
of the skull, emerges by a small foramen in the flat proximal portion of the right frontal 
bone, and thence passes forwards, at some depth from the surface, between the cephalic 
portion of the lateral muscle and the membrane which forms the dorsal boundary 
of the dorsal (left) orbit. It supplies the skin of the extreme anterior end of the 
dorsal fin on the upper side. It seems at first sight that this nerve has changed its 
morphological relations ; for since it belongs to the right side of the head we might 
expect to find its anterior part on the ventral or right side of the interorbital septum, 



70 

with the right orbito-uasal ; whereas it actually runs on what is morphologically the 
ventral side of the left eye, crossing in its course the left olfactory and orbito-nasal 
nerves. But tlie explanation of this apparent anomaly is not difficult. The dorsal 
branch of the fifth is a sensory nerve and was connected in the original symmetrical 
fish with the skin of the extremity of the dorsal fin which was originally j)osterior to 
the eyes. The fin remained behind the eyes during the rotation of the latter, and 
after the left eye had travelled round to the right side, the dorsal fin with the neigh- 
bouring muscles began to extend forwards. Jiut instead of extending forwards along 
the now distorted median dorsal line, the fin grew forward along the edge of the left 
ectethmoid bone, which supports the left eye in its new position, and which is mor- 
])hologically ventral to the left eye. The nerve connected with the fin necessarily 
accompanied the latter in its growth, and thus this nerve comes to be actually dorsal 
and morphologically ventral to the left eye. The origin of the nerve remains in its 
original position posterior to the eyes on the right side of the skull. 

The corresponding nerve of the left side makes its exit from the skull fi-om a corres- 
ponding foramen in the flat proximal portion of the left frontal bone, on the lower (left) 
side of the dorsal fin ; it passes forwards on the left side of the fin to its apex. 

On the ri'dit side the trunk of the fifth nerve, which emerges from the skull through 
the sphenolic foramen, divides immediately after its exit into two large jjranches, the 
maxillary and mandibular nerves. The maxillary branch supplies with sensory fibres 
the skin of tlie upper jaw and also sends motor fibres to the palatal muscle. The 
mandibular branch supplies with sensory fibres the skin of the lower jaw; the largest 
division of it enters a canal in the nuindibular bone, whence it supplies the mucous 
membrane of the floor of the mouth. The main trunk of these two branches, the 
maxillary and nuuidibular, while still within the skull, gives oil" a snuUl nerve which 
leaves the skull by the great anterior opening, and passes forwards below the recti 
muscles of the eye ; it supplies the anterior jiart of the palate and is called the palato- 

nasal. 

On the left side these branches of the fifth are much enlarged, their sensory fibres 
bein" multiplied in proportion to the great development of tactile filaments and 
epidermic sense-organs on this side. The palato-nasal branch reaches this side of the 
head partly through the gap between the ectetlnuoid and parasphenoid, partly through 
a foramen in the sphenotic in front of the large sphenotic foramen. The latter foramen 
is much larger than that on the right side, and the common trunk of tlie maxillary and 
mandibular nerves which passes through it is proportionally large. These branches of 
the fifth on the left side are represented in PI. XV, 2, where the maxillary is indicated 
by V 2, the palato-nasal by V 2a, and the mandibular by V 3. The dorsal branch 
of the fiftli, which accompanies the dorsal fin, is seen passing forwards just above the 

palato-nasul. 

The seventh cranial nerve is called the facial ; its distribution is the same on both 
sides, as it belongs to a region of which the symmetry has not been disturbed. The 



71 

pi-iucipal trunk ol' the facial leaves the skull by a circular foramen in the pronticbone, 
and then passes through a foramen in the head of the hyomandibular. But after this 
it is still covered by the pi-eoperculura, which must be removed before the distribution 
of the nerve can be obsi'r\ed : the facial runs for some distance between the 
hyomandibular and the preoperculum. Soon after its exit from the hyomandibular 
foramen the nerve trunk divides into two branches, the posterior of which is the 
ramus opercularis, the anterior the ramus hyoideo-jnandibularis. The rawns operadaris 
(VII 2a, PI. XV, 2) divides into branches which are distributed to the skin of the 
operculum. The ramus hyoideo-mandibularis divides into two branches, one of which, 
the ramus mandibularis, VII 1, runs along the anterior part of the surface of the 
quadrate. It gives off branches to the jaw-muscle, and into the substance of the 
c^uadrate, and passes through a foramen in the head of the quadrate to the inner side 
of the mandibular bone, where it supplies the transverse mandibular muscle, the oenio- 
hyoid muscle, and the mucous membrane of the floor of the mouth. The other branch, 
the ramus hyoideus, VII 2, bends inwards to reach the iimer side of the stylohyal 
bone, and is distributed to the inner surface of the hyoid arch. 

The eighth cranial nerve is the auditory, which never leaves the interior of the skull, 
but is exclusively distributed to the auditory organ : it is the auditory nerve. 

The ninth cranial nerve is called the glosso-pharyngeal, a name taken from human 
anatomy, but not at all appropriate to the anatomy of fishes. This nerve, like the 
seventh, is distributed in the same way on each side. It makes its exit from the skull 
by a special small foramen in the opisthotic bone, arising from the medulla oblongata 
by an independent root. On the trunk of the nerve, a little beyond its exit from the 
skull, there is a ganglion of considerable size, below which the nerve bifurcates into 
two branches. The anterior branch goes to the posterior surface of the operculum 
and hyoid arch, the posterior to the anterior surface of the first branchial arch. 

The tenth cranial nerve, called nervus vagus, is more widely distributed than any 
of the others, and represents a series of nerves united into a common trunk at their 
origin. The single trunk passes out of the skull through a circular foramen in the 
exoccipital bone, and then divides into several branches. The first branch, the most 
anterior, bifurcates into two, and has a large ganglion at the jDoint of bifurcation ; 
it forks over the second branchial cleft, the front branch going to the posterior face of 
the first l)ranchial arch, the posterior branch to the anterior face of the second 
branchial arch. Similarly the second branch of the vagus bifurcates over the third 
branchial cleft, and has a ganglion at its point of bifurcation. The third branch has 
no ganglion, but bifurcates in the same way over the fourth branchial cleft. The 
fourth branch bifurcates over the fifth branchial cleft, its anterior branch going to the 
posterior face of the fourth branchial arch, its posterior branch to the posterior wall of 
the branchial chamber and the fifth branchial arch. A nerve from this branch goes 
to the heart. The fifth branch of the vagus runs down the oesophagus to tlie stomach. 
The sixth branch is the lateral nerve or nerve of the lateral line : it runs close above 



72 

the vertebral centra on the ventral side of the band of connective tissue which 
separates the dorsal and ventral lateral muscles. From this position it sends off nerves 
which supply the sense-organs of the dermal canal of the lateral line. At its origin 
this nerve gives off on each side a branch which curves upwards and forwards and runs 
immediately beneath the skin along the course of the supra-temporal dermal canal on 
the right side, the series of supra-temporal superlicial sense-organs on tlie left side. 
On the left side there is another nerve given off from the lateral nerve at its origin : this 
nerve runs immediately beneath the skin straight forwards across the side of the lateral 
ridge of the skull : it supplies the superficial sense organs of the epidermis which lie 
alonfj this direction. The two nerves last mentioned are shown in PI. XV, 2, indicated 
as X Ga and X 6b. 

PI. XV, 2, exliibits the cutaneous brancli£s of the cranial nerves on the left side, and 
is intended to show the great development of these branches which has taken place in 
connection with the numerous tactile filaments and epidermic sense-organs which have 
been developed on the skin of the left side of the head. 



73 



CHAPTER V. 

THE SKIN. 

The skin everywhere consists of two layers very diflereut from one another in structure. 
The lower layer, which is much the thicker, consists of fibrous connective tissue, 
forming a dense tough membrane. Tliis layer is about -^th of an inch thick (I mm.). 
It is clothed externally by a thin layer of cells, the longer axis of which is perpen- 
dicular to the surface of the body : this is the epidermis. The lower layer or derma 
contains the scales, the ends of which project backwards through the epidermis, and 
the pigment cells or chromatophores. On the lower side of the head anteriorly the 
skin forms a number of flexible papillte, or filaments, which are delicate tactile organs. 
The skin is continued over the CA'es, but the part which covers the eve is thin and 
perfectly transparent. Scales are present in the skin everywhere, except over the eyes 
and in the region of the tactile filaments. The scales can be detached from the skin 
without difficulty, and when separated and examined with a low power of the 
microscope present the appearance shown in Fig. 1, PL XIV. The largest scales are 
in the central region of the surface of either side. The scales consist of plates of 
fibrous tissue hardened by the deposition of lime-salts. Each has the form of a 
rectangle at the posterior end of which is a portion bounded internally bj- two straight 
lines meeting at an obtuse angle, outwardly by a semicircular curve, and covered with 
sixteen rows of spines. In each row the outermost spine is the largest, the other.s 
becoming gradually shorter : there are five spines in each row, and the rows radiate 
from the angle at which the internal bounding lines of the spinous area meet. This 
spinous area is the onlv portion of the scale which is expo.sed at the surface of the skin, 
the remainder being imbedded in a socket and overlapped by adjacent scales ; they 
are placed with their longer axes directed backwards, and each overlaps the one 
behind it. They are arranged quincuncially, that is, each scale in any transverse row 
lies over the line where the edges of two adjacent scales of the row behind meet one 
another. In consequence of this quincuncial arrangement the transverse rows, which 
are perpendicular to the longitudinal axis of the fish, are not easily recognised ; but two 
series of oblique rows are visible, one series running downwards from right to left, the 
other downwards from left to right. In the same way in the pattern of a wall paper 
when there is a figure repealed at equal distances in lines crossing one another at right 

L 



74 

angles, but arranged quiucuncially, the rectangular lines cannot easily be followed, 
b\it two oblique or diagonal series become conspicuous. It is the oblique rows of 
scales, either those from right to left or from left to right, which are counted in 
descriling the specific characters of a fish. 

Tlie iml)edded portion of a scale exhibits a numljer of parallel curved lines, the 
edges of the lamince of which it is composed. The directions of these lines divide this 
portion of the scale into three areas : a triangular area bounded by the anterior edge 
of the scale and two lines which inaet at an acute angle near the anterior apes of the 
spinous portion, and two similar areas on either side of this. The anterior portion is 
divided up bv a number of radiating straight lines, into radiating strips, ea^h of which 
is occupied by a series of short curved parallel lines. The two other areas are 
occupied by lines parallel to the dorsal and ventral edges of the scale. 

The scales of Solea lascaris, variegata, and bitea resemble those of S. mdgaris in 
structure. The scale of lascaris. Fig. 4, PI. XIV, is the largest : it has the same 
general shape as that of vtdgaris, but the spines are more pointed, and there are 
seventeen rows of them, and six spines in each of the central rows. The scale of 
variegata, Fig. 3, is shorter in proportion to its breadth than that of lascaris, it has 26 
rows of spines, with eight spines in each central row : the spines, except the most 
external, are short and blui^t. The scale of hitea. Fig. 5, is the smallest of the four : 
in shape it resembles. that of mdgaris ; it has 21 rows of spines, four spines in each of 
the central rows ; the spines are rather short and pointed. 

The " lateral line " which runs down the centre of each side of the sole is formed by 
a series of scales which are very different from the ordinary scales of the body. They 
have no spines, and no portion of them projects beyond the surface of the skin. One 
of those scales from Solea tmlgaris is represented in Fig. 2, PL XIV. Anteriorly its 
structure resembles one of the ordinary scales, but posteriorly it is narrowed to a blunt 
apex and the spinous portion is wanting. On its external surface, for a little more 
than half its length posteriorly, there runs a kind of tunnel with rounded roof which, 
with the scale below, forms a tube open at both ends : this tube or tunnel is broader in 
front than behind. In the floor of the tunnel, not far from the posterior end of the 
scale, is a larg(> oval aperture. These scales of the lateral line overlap one another in 
such a way that the aperture in the floor of the tunnel of one is just in front of the 
anterior aperture of the tunnel of the scale behind it. 

Dermal Canals and !>ense-organs. 

This system consists of a inimber of coimected tubular channels running in the 
derma or in bones originally derived from the derma. The longest and most easily 
observed of these tubes runs beneath the lateral line. It is lined by a cellular layer 
somewhat similar to the superficial epidermis, aiul it runs through the series of bony 
tubes just described as belon<>ing to the scales of the lateral line. Tracing the tube 



75 

from before backwards we find that the tube enters the anterior end of the tunnel on 
each scale and passes through the aperture in the floor of the tunnel to enter the 
tunnel of the next scale, and so on. But before passing through the aperture in the 
floor of the tunnel the tube gives off a branch which continues to run through the 
tunnel to its posterior aperture, and passes beyond the scale to open by a pore on the 
surface of the skin. Thus corresponding to each scale of the lateral line there is a 
pore in the skin which leads into the dermal tube of the lateral line. The course of 
che tube and its relation to the scales are exhibited in Fig. 6, PI. XIV, which 
represents an ideal longitudinal section of the skin along the lateral line : sc. indicates 
the scales in section, d.t , the tube, p, the external pores. The left end of the section 
is the anterior. On the inner wall of this lateral dermal tube are a number of sense- 
organs supplied with branches of the nervus lateralis, which in the sole as in the 
majority of fishes is a branch of the vagus. If Ave follow the lateral dermal tube 
forwards we find that at the side of the back part of the skull, over the parietal crest, 
it becomes separate from the skin and enters the hinder branch of a triradiate bony 
tube : one branch of this bone passes straight forwards for a short distance and then 
terminates, and the lateral tube then enters a tube in the pterotic boue. This tube 
excavated beneath the surface of the bones of the skull is continued forwards, sometimes 
opening into a groove on the lateral ridge of the skull : it passes just above the 
posterior corner of the sphenotic bone, and then enters the outer edge of the posterior 
half of the frontal ; then it is continued as an enclosed tube through the interorbital 
process of the frontal, and emerging from this enters a separate tubular bone similar 
to that which lies on the outer surface of the parietal crest. This bone bifurcates each 
branch ending in the skin, probably by an opening to the exterior. Tliis last bone is 
the nasal : the former ma}^ be called the supra-temporal bone. [See Fig. A on the 
following page.) 

It follows of course from the peculiar modification of the frontal Ijones that the 
cephalic portion of the lateral tube on the left side, following the course of the left 
frontal bone, passes from the apparent left side of the head to the right : morpho- 
logically of course it retains its proper relations, but as it passed originally dorsal to 
the left eye, it has been pushed over by the movement of that eye to the right side, 
and so comes to lie to the right of the anterior part of the dorsal fin. But the left 
nasal bone is on the left side, for the tube after leaving the left frontal bone bends 
beneath the anterior dorsal interspinous bone, to the left side of the snout : thus the 
left nasal bone is attached to the skin in front of the nasal capsule of the left side. 
The right nasal bone lies in front of the nasal capsule of the right side. 

The supra-temporal bone, besides its posterior and anterior openings, has two others, 
a dorsal and a ventral. The dorsal opening is at the end of a short branch, and leads 
into a tube in the derma surrounded by modified scales, and in all respects resembling 
the tube of the lateral line : this supra-temporal dermal tube in fact lies under and is 
the cause of the supra-temporal branch of the lateral line described with the external 



leatures of the sole. Tlie ventral opening of the supra-temporal bone leads into a 
membranous separate tube, which passes beneath the skin in a ventral direction, runs 
through a tube which pierces the preopercular bone, and is continued forwards to the 
mandible. 

Kow the supra-temporal tubes are, as we have seen, dermal, and pass through 
apertures in a series of scales similar to those of other parts of the skin in structure. 
On the right side the supra-temporal tube retains this structure throughout up to its 
termination at the extreme apes of tlie snout. But on the left side anteriorly the 
scales disappear, and tlie supra-temporal tube opens out on to the surface, its sense 
organs becoming quite superficial : they are situated between the bases of the tactile 
iilaments of the lower surface of the snout. 

In the cod [Gad us morr/ma) the lateral cephalic tube gives off another branch 




Fig. A. A diagram to illustrate the distribution of the epidermic sense-orgnns and dermal tubes on 
the head of the sole, a, the anterior continuation of the lateral tube; t, the supra-tempoi-al tube; 
c, the preopercular tube; (l\ the suh-ocular organs of the left side; I, the lateral Hue tube; 
r.n., right nasal bone ; l.n., left nasal bom; ; t, the supi-a-temporal boue. 

besides those already mentioned, namely a sub-ocular tube, which is enclosed by a 
series of scale-like bones, the sub-orbital bones. This sub-ocular branch is found in 
the plaice [Pleuronectes platessa) on the right side as a canal in the derma beneath 
the ventral eye ; while on the left side it exists as a dermal tube between the mouth 
and tlie supra-temporal tube. In the sole I have been unable to find a trace of the 
sub- ocular tube on the right side, but on the left side it is represented by superficial 
epidermic sense-organs distributed all over the skin between the cleft of the mouth 
and the sense-organs of the supra-temporal 11 lie. In the sole there are in addition a 
number of superficial sense-organs along the line of the pre-opercular tube, forming a 
single series along the upper part of that tube, and spreading out over the whole area 
l)eliind the mouth- cleft below. 

The lateral cephalic tube and the pre-opercular tuljc, which are to a large extent 
enclosed in solid bone, nevertheless commuuicate at intervals with the exterior by 



77 



means of short tubes wliicli open on the surface of the skin ; the supra-temporal and 
sub-ocular dermal tubes where they exist, are also connected by short tubes with 
superficial pores, so that all the tubes of the sj'stem are related to the skin in almost 
the same way as the tube of the lateral line. The cephalic tubes also in allprobability 
contain sense-organs similar to those of the lateral tube. The tubes of the head are 
innervated by branches of the cranial nerves. The supra-ocular part of the lateral 
cephalic tube receives branches from the orbito-nasal nerve, the sub-ocular tube is 
innervated by branches from tlie maxillary and palato-nasal nerves, the pre -opercular 
tube is supplied from the seventh or facial nerve. There is little doubt that the 
lateral and pre-opercular cephalic tubes, now enclosed in solid bone, were, like tlie rest, 
originally dermal tubes enclosed by tubular scales. In fact, the bones through which 
they pass represent dermal scales fused together. The tubes and the bones thus 
produced have sunk beneath the skin, and the bones have become part of the skull. 




Pig. B. A diagram to illustrate the distribution of the dermal tubes in the head of the cod. Letters 
as in the diagi-am of the sole. 

But all these dermal tubes at a still earlier period were part of the external surface of 
the skin. The sense-organs of the tubes and their epithelium are really derived fi-om 
the epidermis. In some cases the organs of the lateral line are superficial throughout 
life, for example, in the gobies and tlie mullet, and in all cases they are developed in 
the embryo or young fish in the external epidermis. The tubes are formed both in 
evolution and development by the deepening and ultimate enclosure of grooves on the 
surface which include the sense-organs. 

In the cod, which may be taken as exliibiting pretty nearly the original condition 
of the cephalic tubes of the sole and other flat-fishes, there are no superficial sense- 
organs on the head, and the tubes of the two sides are symmetrically arranged. 



78 

The diagram, Fig. B, shows the position and the relations of the cephalic tubes in 
that species. The supra-temporal tubes are short, and are surrounded by thin tubular 
scale-like bones. The sub-ocular tube is also enclosed in a series of tubular bony 
scales, the sub-orbital bones. Both these and the supra-temporal bones, though 
homologous with the ordinary dermal scales, are not similar to them, having a much 
larger size and deeper position. 

In the sole the changes which have taken place in the course of evolution are as 
follows : The supra-temporal tubes have become much elongated, having grown 
forwards with the anterior extension of the dorsal fin till they reach the extremity of 
the snout. On the right side the tube is no longer enclosed by peculiar scale-like 
bones, but by tubular dermal scales, closely resembling the ordinary scales of the skin. 
On the left side of the head, the scales having disappeared anteriorly, the supra- 
temporal tube has opened out on to the surface, and the sense-organs which belong to 
it have become superficial. The two supra-temporal tubes are symmetrical in relation 
to the two sides of the dorsal fin, but entirely asymmetrical in relation to other parts 
of the head; for in consequence of their relation to the fin they both lie morpho- 
logically ventral to the left eye, between the left eye and the mouth. 

The lateral cephalic tube of the left side has been distorted by the change of 
position of the left orbit. Its posterior part retains its original position, but its 
anterior or supra-ocular part lying in the inter-orbital process of the left frontal bone, 
bends round towards the right side and runs close beside the right supra-ocular tube 
between the two eyes. 

The sub-ocular tube of the right side has disappeared; that of the left side is 
represented by the immerous superficial sense-organs which lie above the mouth on 
the lower side of the head. 

The two pre-opercular tubes remain in their original position, but on the left side a 
i\umber of superficial sense-organs have been developed over the region of the 
j»re-opercular tube. This is, in some respects, one of the most remarkable of the 
peculiar developments in the head of the sole. It is intelligible that a dermal tube 
originally derived from a superficial groove should again become superficial ; but it is 
surprising to find surperficial organs developing anew, outside a tube which contains 
similar organs originally derived from the siiiface. 

The supra-temporal tubes are innervated by a long branch from the lateral nerve 
belonging to the vagus. On the left side a similar branch of the vagus passes 
forwards towards the sub-ocular sense-organs. Along the proximal part of the course 
of this nerve is a single series of superficial sense-organs, which lies over the proximal 
pai-t of the lateral cephaUc tuljes. I have not been able to decide whether this series 
really belongs to the sub-ocular series of the left side, or bears the same relation to the 
proximal part of the lateral cephalic tube as the pre-opercular superficial organs to 
the pre-opercular tube. In studying the relations of the mucous tubes and epidermic 
sense-organs in the head of the sole, I have been very greatly assisted by a jjaper by 



Dr. Eainsay H. Traquair, publialied in 18G5." The sole is not considered in this 
paper, but the interpretation of the distribution of the orrraiis and canals in this 
species is comparatively easy after Dr. Traquair's lucid explanation of the derivation 
of the arrangements found in other flat-fishes from the original symmetrical condition. 
The diagram of the arrangement in the cod which I have given is copied, with 
slight modifications, from Dr. Traquair's ; and my diagram of the arrangement in the 
sole is constructed on the same plan as his diagrams of the arrangements in the plaice 
and other species. 

Minute Structure of the Skin, Dermal Tubes, and Sense-orrjans. 

When thin sections of the skin are prepared and examined under the microscope, 
the derma is seen to be composed of a number of sheets and bands of felted fibres, as in 
PI. XIV, 6. In my preparations no nuclei are visible in this tissue, Init the pieces of 
skin were decalcified in weak nitric acid before they were cut, in order to remove the 
lime from the scales, and the action of the acid may have somewhat altered the 
condition of the fibrils. The scales, as seen in section, consist of thin lamince lying one 
upon another ; the laminae are entirely homogeneous in structure, and seem to be 
simply sheets of the fibrous tissue which have been consolidated and then impregnated 
with calcareous salts. The scales are contained in cavities of the fibrous tissue. In the 
preparations the fibrous tissue is separated slightly from the surface of the scales, but 
this is doubtless due to the shrinking produced by the process of preparation, and in 
life the fibrous tissue is in contact with the surface of the scale. Above the scales 
there is a layer of delicate spongy fibrous tissue in which the fibres are short, and run 
in a vertical as well as a longitudinal direction ; this reticular tissue contains 
numerous nuclei. This tissue separates the external surface of the scale from the 
dense fibrous laminated tissue, while the internal surface of the scale is in immediate 
contact with the latter. The epidermis consists of several, six or seven, layers of cells. 
At the base of the epidermis the cells are polygonal and as broad as they are high : 
each cell contains a large nucleus, which becomes deeply stained under the action of 
staining liquids. Towards the outer surface most of the cells become thin and flat, 
as in the human epidermis, but in preparations a certain number of them are large 
spherical vesicles. These are mucous cells. The surface of the sole as of most other 
fishes is, during life, always covered with a certain amount of slimy mucus which is 
derived from the epidermis. This mucus is produced by the discharge of the contents 
of the globular mucous cells just mentioned. The cells at the base of the cpidermLs 
are constantly multiplying and growing, and in consequence the outermost of them 
are gradually pushed to the surface. The superficial layers are as constantly broken 
down and, as it were, dissolved away, some of the cells becoming, before they reach 
the surface, converted into capsules of mucus, and this mucus, together with the 

* "On the Asymmetry of the Pleuronectidoe, as elucidated by an Examination of the Skeli'tou in 
the Turbot. ILiIibnt, and Plaice." (-'Trans." Lin. Sue, vol. x.xv.) 



8(. 

debi-is of the other superficial cells, forms the slimy coating of the fish's skin. There 
are no special glands connected with the skin of the sole. 

In the outermost layers of the fibrous derma, immediately beneath the epidermis, 
are situated the pigment cells or chromatophores. Some chromatophores are also 
found in a deeper po.sition, in the fibrous tissue which lies between the deeper parts of 
the scales, but no pigment is found below the level of the skin to which tlie anterior 
edges of the scales reach. The epidermis and the thin subjacent layer of the derma, 
which contains the chromatophores, are continued over the exposed portions of the 
scales, with the exception of the longest most posterior spines of the scales : these pierce 
through the skin and epidermis and project beyond the latter. 

The appearance of a longitudinal section through the dermal tube of the lateral line, 
magnified 40 times, is shown in Fig. 6, Plate XIV. In other parts of the skin muscles 
are of course found below the derma, but the dermal tube of the lateral line lies 
directly above the connective tissue partition between the dorsal and ventral lateral 
muscles, and the connective tissue of this partition passes directly into the skin. 
The fibrous tissue of this partition contains large spaces occupied by loose 
reticular tissue the meshes of which are large and filled during life with lymph;' 
this tissue is seen in the lowest part of the figure. The figure includes one whole scale 
of the lateral line and parts of two others ; the three pores, p,p,p, corresponding to 
these scales are seen leading into the dermal tu])e. The section passes longitudinally 
through the centre of the dermal tube and therefore the roof of the tunnel formed by 
each scale is seen above the dermal tube, and the floor below it. The dermal tube is 
seen bending down to pass through the hole in one scale to enter the tunnel of the 
scale behind it ; beyond the hole in the floor of the scale a branch of the dermal tube 
passes backvvards to open on the surface at the external pore. The dermal tube is 
lined by an epithelium which is only separated from the surface of the scales by 
a very thin fibrous membrane. This epithelium is continuous with the epidermis at 
the external pores, but diflers much from the epidermis in character. It is of verj- 
slight thickness, consisting only of two or three layers of cells. The lowest layer 
consists of small undifTerentiated cells which grow and multiply, continual!}' 
replenishing tlie outer layers. Nearly all these outer cells are globular and vesicular; 
that is they form hollow capsules, doubtless containing nuicus. During life the dermal 
tube contains mucus, which is the product of this epithelium. But at certain places 
this epithelium contains sense-organs, consisting of portions of the epitlielium which 
have an entirely diflerent structure and function. The cells of the sense-organs are not 
secretory but sensory, and they are connected with nerve fibrils. One of these sense- 
organs, as seen in longitudinal section, is shown at s.o, in PI. XIV, G. It is situated on 
the inner wall of the dermal tiil)e, and lies on the floor of the tunnel of a scale a little 
in front of the hole through which the dermal tube passes to the next scale. At a point 
near the anterior and deep border of the scale containing the sense-organ there is a 
small aperture in the scale through which a nerve passes from the skin below the scale. 



81 

This nerve (n, Fig 6) runs posteriorly along the surface of the scale, beneath the 
epithelium of the dermal tube, to the sense-organ. The sense-organ consists of a 
number of thin elongated cells placed so that their length is almost perpendicular to the 
wall of the dermal tube. Each of these cells contains in its lower portion a spindle- 
shaped swelling which contains a nucleus. One end of each cell reaches the surface of the 
sense-organ, and the other reaches its basement membrane : the cells are all in contact, 
the nuclear swellings being so arranged that the cells are packed in the least possible 
compass. Thus the nuclear swelling of one cell is at its base, that of the next some- 
what higher up, so that the nuclei form two rows, and the nuclei of some of the cells 
are even higher still, forming a third row. But it is only the nuclei wliicli are in two 
or three layers, the cells are all in a single layer side by side. The nuclei, in spite of 
the arrangement described, occupy more space than the cells, and consc^qnently the 
base of the sense-organ is broader than its surface, so that only the central cells are 
straight, the external cells curving at their upper ends towards the centre of the sense- 
organ. The upper end of each cell ends in a delicate protoplasmic hair which projects 
into the cavity of the dermal tube. The lower end of each cell is continuous with one 
of the ultimate fibrils of the nerve previously mentioned. I have not made out this 
connection in all the cells, but I have traced it in some, and l:)elieve that it exists in all. 
In some preparations a kind of clot is seen on the surface of the sense organ, and 
sometimes this seems to have separated from the surface of the organ, breakino- ofTthe 
sensory hairs and taking them with it. This clot often present a laminated appearance, 
as if formed of thin layers one over another. It has been seen in some fishes in an 
organ examined in a perfectly fresh condition. Prof. Emery* concludes that the lamince 
of the clot, which is generally called the cupula, are successive cuticles secreted by 
the peripheral cells of the sense organ. I think it is difficult to accept this conclusion, 
and am inclined to think the cupula is, during life, of a mucous nature, and therefore 
semi- liquid. It seems certain that the sensory hairs are imbedded in the cupula. It 
is difficult to understand how such cells as those of the sense-organ sliould secrete 
mucus or form a cuticle : perhaps the cupula is nothing more than the ordinary mucus 
of the dermal tube which keeps a constant position in preparations because it is retained 
by the numerous sen.sory hairs. 

There is not a sense-organ to every scale of the lateral line ; in the middle of the 
body there is a sense organ on every third scale, that is to say, there are two scales 
bearing no sense-organs between two scales which bear them. The position of the 
sense-organ in relation to the scale on which it is situated is always the same. 

The function of these sense organs is still entirely imknown. It has been suggested 
that they convey to the fish a sense of its position in the water, and so enable it to 
retain its vertical position, but the evidence for this is not very conclufive : if it were 
true we should expect to find the organs atrophied in the flat fishes which have 

* ■' Fauna nnrl Flora de.s Golfes von Xeapel." " Fierasfer." 



82 

abandoned the vertical position altogetlier. What stimulus afTects the organs it i.-* 
difficult to imagine : and it is also difficult to understand how the sensory hairs act 
immersed as they are in the substance, whether it be mucu.s or not, which forms the 
so-called cupula. But that these organs are of great importance to aquatic vertebrates 
there can be no doubt, since they occur not only in all kinds of fishes but in aquatic 
Amphibia : they are even present in the tadpole and other larval batracliians so long 
as they retain their aquatic respiration. 

These sense-organs are in all cases first developed in the superficial epidermis ; the 
development of the dermal tube in which they are enclosed takes place subsequently. 
The dermal tube is formed from a superficial groove which appears on the surface of 
the skin along the line where the sense-organs are situated. The groove becomes 
deeper and its edges meet over it and coalesce everywhere except where the pores are 
left by which the tube communicates with the exterior. In some fishes, e.g., Gobius, 
the sense-organs remain superficial tluuvighout life, no lateral dermal tube being 
developed. 

As I have already mentioned (p. 7G) there are also a number of superficial sense-organs 
on the under side of the head of tlie sole. These organs are situated in the depressions 
between the villi or tactile filaments with which the skin in this region is provided. 
The minute structure of this part of the skin is illustrated by Fig. I, Plate XV, 
which is drawn from a section of the part of the skin above the posterior half of the 
mouth cleft on the lower side of the body. Some of the filaments are long and slender, 
others short and blunt. Eunning up the centre of each filament is a sausage- shaped 
supporting rod which is composed of a tissue having the structure of fibro-cartilage. 
In section this body exhibits fibres anastomosing with one another and running in a 
direction transverse to the longer axis of the rod. These fibres contain nuclei, and 
the interspaces between them are filled l)y a homogeneous solid substance of the 
nature of cartilage. These supporting rods belong to the derma. The epidermis is 
continued over the filament, l)econiing thinner at the apex, and between the supporting 
rod or core and the ei)idcrmis is a continuation of the fibi'ous tissue of the derma. 
Eunning up the sides of the supporting rod are several fine nerves. These nerves send 
off fibrils which branch, and tlu-ir ultimate ramifications enter the epidermis. There 
are no special sense-organs of any kind in connection with these nerve fibrils : the 
ultimate termination of the fibrils I have not been able to trace : they penetrate between 
the cells of the epidermis, and doubtless ultimately come into connection with some of 
the epidermic cells. Nerve-fibrils are known to eiiter the epidermis in the same way in 
the skin of the tip of the human finger, and in all probability help to give that skin its 
delicate sense of touch. I have indicated the connection of the ultimate nerve-fibrils 
with the epidermis on the right side of the figure. On the left side of the figure 
are sections of four short blunt filaments which do not project far beyond the surface 
of the skin. Around tlie cores of these, besides the black lines indicating parts of 
nerves, is a coarse stippling which represents the appearance of a curious granular 



83 

tissue occurring iu lliis position in all llie lilanicuts. This tissue obscures the nerve 
fibres and makes it somewhat difficult to follow out their course iu the sections. The 
sections from which the present description is taken, and one of wliich is represented 
slightly diagrammatically by the figure, were prepared from pieces of skin treated when 
fresh with chloride of gold. This reagent stains the nerves black or violet, and aflects 
the remaining tissues slightly or not at all. Thus the nerves can be traced through the 
granular tissue just mentioiied. Tlie granular tis.sue is somewhat opaque, consisting of 
irregularly branched cells the contents of which are coarsely granular. These cells 
exactly resemble iu structure the chromatophores of the right or coloured side of the 
body, but the}' are not coloured. In fact, to use a seeming paradox, these cells are 
colourless chromatophores ; that is to say, they are chromato])hores of which the granules 
instead of being black or orange ai-e white and opaque. 'J hus the white colour of the 
under side of the sole is not due to the absence of chromatophores, but merely to the 
absence of what is usually called colour in the chromatophores; the pigment cells are 
not absent from the skin of the lower side, but are bleached. It is a very connnon 
thing to find coloured blotches on the lower side of a sole, and from the above it is 
evident that these coloured blotches are not due to the development of chromatophores 
iu certain areas while they are absent elsewhere, but are due to the fact that the 
chromatophores in these areas are coloured, while in the rest of the skin of the lower 
surface the}' are white. 

One of the superficial epidermic sense-organs of the under side of the head is 
represented in section in the figure. It will be seen that they do not differ in structure 
from the sense-organs of the dermal tube of the lateral line. The sensory hairs are 
present in these organs, though not shown in the figure, as they are not well jireserved 
by the chloride of gold method of preparation. 



M 



84 



CHAPTEI! Vr. 
EMBEYOLOGY. 

The ripe ovum of Solea vuhjarU after it lias been removed from the bocly of the fish 
and is floating in sea water, and wlu-n it has not been fertihsed, has tlie followinir 
structure: The whole ovum is a spherical transpai'ent body measuring \\1 to 1'51 
mm. ('05 to '06 inch) in diameter, the size of different eggs varying within these 
limits. The ovum consists of a definite thin transparent membrane surrounding a 
solid mass ; the former may be called the vitelline membrane, the latter the ovum in a 
stricter sense of the word. The whole of the egg with its envelope corresponds only 
to the yolk of a hen's egg, there is nothing about it which represents the " white " or 
the shell of the latter. The yolk of a hen's egg is surrounded by a thin membrane of 
its own which corresponds to the vitelline membrane of the sole's eg^. The ovum 
])roper within the vitelline membrane consists of two different parts : a smaller 
somewhat protuberant portion which is more granular and less transparent, and a 
more transparent larger portion. Tlie former is the germ (blastodisc), and consists of 
living organic matter known as protoplasm. Tiiis germ is actually alive, and it 
exhibits spontaneous movements and changes which gradually lead to the formation of 
the young fish, while the larger portion is the yolk, and is simply a supply of very 
nutritious food on which the germ lives and by means of which it grows. TJie yolk is 
in fact gradually aljsorbed by the embryo during its development. In consequence of 
the protuberance of tlie germ, the vitelline membrane being stiff and spherical, tliere is 
a space between the membrane and the surface of the ovum all round the junction of 
the germ with the yolk : this is the perivitelline space. Immediately lieneath the germ 
the yolk is divided up into large separate masses of a cubical sliajie : these masses 
form a single layer, the rest of the yolk being undivided. The yolk is more or less 
liquid, and it is confined within a delicate pellicle of protoplasm which extends from 
the edge of the germ all round the yolk. Thus the yolk is really contained williiii the 
protoplasmic germ. In fact the germ is the essential part of the ovum; some animals 
produce ova without either membrane or yolk : the yolk is to be regarded as an 
accumulation of food material within the protoi)lasm ol a reproductive "cell" or plastid. 
On the surface of the yolk, immediatel}' beneath its protoplasmic pellicle, are several 
groups of minute oil globules. On account of their refracting power these appear 



8.') 

opaque white by rellected light and durii. by traiisiuiLLed hghl. They represent an 
excess of fatty matter belonging to the yolk. 

I have not seen the ripe ovum of the sole immediately after its escape from the ovary. 
But the ova of other flat-fishes have been studied by myself and others immediately 
after extrusion, and it has been found, e.g., in the cod and the flounder, that at first 
the germinal protoplasm is not aggregated into a protuberant mass, but is more 
extended over the surface of tlie yolk, and that the vitelline membrane is everywhere 
in direct contact with the ovum. The aggregation of the protoplasm into a distinct 
germinal mass and the consequent formation of the perivitelline space take place after 
the extrusion of the ovum, and take place in the same way whether the ovum is 
fertilised or not. 

I have not particularl}- studied the spermatozoon of the sole, but have observed it 
sufficient^ to state that it does not differ in structure in any important respect from 
that of other flat-fishes. The milt is very scanty in quantity and thin and transparent 
in appearance, but its peculiarities will be considered in connection with the subject of 
the artificial propagation of the species. I have given a figure of the spermatozoon of 
the dab, Pleitronectes limanda, PL XIII, 7, having accidently omitted to make a drawing 
of that of the sole. In all bony fishes (Teleostei) the head of the spermatozoon is pear- 
shaped, the pointed end being directed forwards in motion. The long slender vibratile 
filament or " tail " is attached to the broader end of the head. The spermatozoa are 
exceedingly small, quite indistinguishable to the unaided eye, but when the fresh 
milt is placed under the microsco]3e multitudes of them are seen actively lashing 
themselves about in all directions. The total length of a spermatozoon of the sole is 
about xo-Qotli'' of ^^ '\nc\x ("07 mm.). 

Fertilisation of the ovum usualh' takes place immediately after extrusion, and 
consists in the entrance of a single spermatozoon into the germinal protoplasm. I 
have not studied the details of the process in the sole's ovum, but have done so in the 
ova of the dab {Pleuronectes limanda) and another species [PI. ojnoglo.ssus). The 
process in the sole is doubtless the same as in these species, and is as follows : Over 
the centre of the germinal protoplasm there is a minute aperture in the vitelline 
membrane which is called the microp}'le. Through this ajDerture a spermatozoon passes, 
and penetrates into the germinal protoplasm. In the latter is the nucleus which, as 
the ovum matures, becomes indistinct, and can only be made visible by coagulating 
the protoplasm with acetic acid or some other chemical reagent. This nucleus can 
also be stained, as it absorbs colouring fluids, such as solutions of carmine, to a greater 
extent than the surrounding protoplasm. The nucleus before fertilisation is complete 
passes to the surface of the germ and gives off in succession two small portions of itself, 
the polar bodies, which are expelled from tlie ovum. The nucleus after this forms the 
female pronucleus, and the head of the spermatozoon which has entered the germ 
forms a similar minute body, the male pronucleus : these two unite into a single 
nucleus, the segmentation nucleus 



80 

The fertilised ovum ol' llie sole, then, jjossesses the same stiucture as was above- 
described in the unfertilised, aud also something not mentioned in the previous 
description, namely, a nucleus in the germ formed by the coalescence of two pronuclei, 
one derived from the nucleus of the unfertilised eg^:, the other from the head of a 
spermatozoon. 

The first visible change which takes place after fertilisation is the division of the 
germinal mass into a number of small segments. The mass first divides into two 
halves separated by a superficial furrow extending across its middle. Another furrow 
then appears crossing the first, so thai the mass is divided into four portions. Each of 
these divides again into two and then into four, so that there are now sixteen segments. 
Then divisions take place in a direction parallel to the surface of the mass, so that it 
comes to consist not of one layer of segments, but of several layers. As this process 
of segmentation continues the segments continually become smaller, so that the 
condition is reached which is seen in Plate XV, Fig. 3. During this time movement of 
the protoplasm on the surface of the yolk and between the yolk segments has caused the 
latter to extend somewhat beyond the edges of the germinal mass. 

The mass of protoplasmic segments into which the original single large mass has 
thus been converted now begins to become thinner and broader, extending itself 
so as to envelop the yolk, us in Plate XV, Fig. 4. When lliis })rocess begins a cavity 
is formed between the yolk and the central part of tlie germinal mass. The germinal 
mass as it extends over tlie surface of the yolk soon becomes so thin that it must now 
be called the germinai membrane (blastoderm). Fig. 5 shows the stage at which the 
germinal membrane has enveloped more than half the yolk. The external part of the 
irerminal membrane for some distance from the edue is thicker than the central 
portion : this tliicker portion rests upon the yolk, while the central part is separated 
from the yolk by the flat cavity already mentioned. This cavity is not exactly in the 
centre of the membrane, the thicker external ring extending farther inwards (on the 
right of Fig. 5) at one point than elsewhere : this broadest part of the germinal ring is 
also the thickest part, and it forms the rudiment which will give rise to the upper or 
dorsal })art of ilie body of the young lish. It nni.st Ije observed tliat tlie layer of yolk 
segments extends jyari passu witli the germinal inenibrane, aud that llic patches ni oil 
'dobules are alwavs at the edjjfe of the extendinsf membrajie. 

As the germinal membrane continues to extend the circumference of the germinal 
ring of course gets smaller ; the rudiment of the young fish above menticjned remains 
with its internal extremity in the same position, continually increasing in length as the 
edge of the nuMul)rane extends over the yolk, until when the yolk is completely 
enclosed, the whole of the germinal ring has been taken uj) into this ludiment. The 
dorsal rudiment by this time has become much thicker and forms an almost cylindrical 
rod, from the sides of which the germiiuil membrane extends over the yolk. The oil 
♦^lobules are now arranged beneath the sides of the dorsal rudiment, while the volk 



87 

segments fonn a layer exteudiug over the whole surface of the j'olk. The end of the 
rudiment which was originally turned towards the centre of the germinal membrane 
becomes enlarged and forms the head of tlie iish ; the point where the edges of the 
membrane closed together forms the posterior end. After a short time two spherical 
masses are seen defmed in the head of the embryo : these are the first rudiments of the 
eyes. The centre of the dorsal rudiment begins to be divided by transverse divisions 
into segments: these segments are blocks of tissue which will afterwards form the large 
lateral muscles of the fish. At the tail end a small round cavity appears, which 
afterwards becomes part of the cavity of tiie intestine. These various structures are 
seen in Plate XV, Fig. 6, and Plate XVI, Fig. 1, one of which shows a profile, the other 
a ventral, view of the embryo at the stage now described. 

At this stage scattered black dots have appeared on the external surface of the dorsal 
rudiment, extending out over the surface of the yolk some distance from the sides of 
the latter. These are pigment cells, and are situated in the skin : they are usually 
called chromatophores. 

What I have called the dorsal rudiment is the solid dorsal portion of the young fish 
containing the rudiments of the brain and spinal coi'd, of the backbone below these, 
and of the lateral muscles at the sides. The yolk sac represents the abdomen of the 
young fish. The intestine is formed as a simple tube beneath the dorsal rudiment 
resting on the surface of the yolk. It is at first closed at each end, neither mouth nor 
anus being yet formed 

After this stage a cavity appears at the anterior end of the embryo between the 
germinal membrane and the yolk. The segmentation cavity previously described 
ceased to be visible after the envelopment of the yolk by the germinal membrane, the 
latter having come into contact with the former. The cavity which now appears has 
exactly the same position as the segmentation cavity. The embryo grows out 
posteriorly, forming a tail which is independent of the yolk sac. The black chromato- 
phores increase in number and extend over the whole surface of the yolk sac, al the 
same time they become branched, sending out short branches in all directions so as to 
assume a stellate fornr. Other chromatophores also appear in addition which are of a 
yellow colour, appearing darker when seen by reflected light. These changes are seen 
in Plate XVI, Fig. 2. 

As the tail increases in length a fold of the skin is formed in the middle line alongf 
its dorsal and ventral edge ; the dorsal fold extending to the head of the embryo. The 
other changes which have taken place by the time the young fish is hatched will be 
understood by reference to Plate XVI, Fig. 3, which shows the fish immediately after 
hatching. The yolk is now considerably diminished and the intestinal tube opens 
behind it by the anus. The tail measui'ed from the anus is as long as the distance 
from the anus to the front of the head. The wide membranous fold is seen extending 
along the middle ventral line of the tail and along the median dorsal line of the fish to 
the back of the head: this is the primordial median fin. There is still no n;outh. 



88 

Behind the eye is a small oval cavity containing two specks. This is the primitive ear, 
the black specks being small particles of carbonate of lime formed within the auditory 
cavity. Beneath the throat is seen a small tubular structure, which in the living young 
lish pulsates regularly : this is the heart. From the line where the wall of the yolk sac, 
or abdomen, joins the body there projects a semicircular membranous fold, which is 
the beginning of the pectoral fin. No indication of the pelvic fins is yet present. The 
trunk of the young fish is seen to be divided by a series of curved transverse lines : 
these are the divisions between the muscular masses of which the trunk muscles are 
composed. A kind of tube runs down the centre of the body, the contents of which 
show a recticulate structure. This tube is the notochord, which contains gelatinous 
material in a number of cavities divided from one another by thin partitions like the 
cavities of a sponge. No bone is yet formed, but the vqrteljraj when they develop 
arise as a series of bony rings formed round the notochord. Tlie chroma tophores are 
now much more abundant than in the embryo before hatching ; there are still only 
two kinds, the black and yellow, and both are much branched ; the two kinds are 
evervwhere mingled together. The pigment is abundant in the primordial median fin, 
except at its posterior e.Ktremity. 

Fig. 4 is a drawing from another recently^hatched sole, a few hours older than that 
.shown in Fig. 3. It will be observed that this figure shows the left side of the fish, 
while Fig. 3 shows the right side, and that the two sides correspond in all respects. 
The newly-hatched sole, or larva of the sole as it may be called, exhibits perfect 
bilateral symmetry and therein resembles the adults of the greater number of marine 
fishes. In Fig. 4 the olfactor}- organ is seen in front of the eye : it is on each side a 
simple rounded cavity opening by a small aperture to the exterior. 

It may be explained here, though it is not evident in the figures, that tlie cavity 
surrounding the yulk in the larval sole contains primitive l)lood; this ])rimitive blood 
contains minute colourless corpuscles, but no red corpuscles, which are not formed till a 
later stage. The posterior end of the heart is open to this cavity, and the blood is 
propelled from the cavity along the vessels at the side of the throat into the aorta 
which runs beneath the notochord, and from the aorta to the cavity again. 

The newly-hatched larva is from 3"o5 to 3'7.5 mm. in length (•14'2 to '15 inches), or 
Ijetween one-seventh and one-sixlh of an inch, and al)out two and-a-half tiiiies as long 
as the di.ameter of the ovum. 

Up to this point the stages t)f development have been descril)ed as they are seen in 
the living egg or newly-hatched fish, and all the figures referred to are fiom drawings 
made by the aid of the camera lucida with a low power of the microscope. But, 
although I have not studied the subject especially in the egg of the sole, it will be con- 
venient here to give a brief description of the internal processes of development so far 
as they are known to occur in the eggs of fishes. 

The germinal ring when examined by means of prepared thin sections is found to 
consist of three lavers of cells. The outermost, which is two cells thick, is called the 



89 

epiblast, and gives rise to the epidermis and otlaer organs, tlie innermost, which is only 
one cell thick, is called the hypoblast, and gives rise to the intestine, the middle layer is 
called the mesoblast, and gives rise to the bones, muscles, and blood vessels. In the 
dorsal rudiment the same three layers are found, but the epiblast is here thickened into 
a great keel which extends inwards and causes the projection of the rudiment; the 
greater part of this keel ultimately separates from the extreme outer layer and forms 
the brain and spinal cord. In the centre of the rudiment beneath the keel is a 
cylindrical rod of cells which become converted into an elastic supporting structure, 
the notochord. Eound the yolk, when it has been completely enveloped, there is a 
layer of protoplasm containing nuclei, but not divided up into cells. The hypoblast 
rests on this layer which is called the periblast. In the ventral region of the developing 
embryo there is nothing but epiblast separated from the periblast by the flattened 
cavity previously mentioned and called the segmentation cavity. The hypoblast bends 
round and forms a straight tulje which lies in a depression in the periblast. This tube 
is the intestine, and when first formed has neither anterior nor posterior opening, 
neither mouth nor anus. The swelling of the anterior part of the epiblastic keel forms 
the brain and causes the protuberance of the head. The sense organs are formed by 
thickenings of the epiblast: these thickenings become hollow and globular and, sinking 
into the interior part of the head (except the nasal organs), become connected with the 
brain by the sensory nerves. The nasal organs become cup-shaped, their cavities 
being open to the exterior by a single aperture each, which is ultimately divided 
into two, the two nostrils of each organ. The heart is formed from mesoblast which 
extends below the front part of the intestinal tube ; it opens posteriorly at first from 
the segmentation cavity, but when the yolk is absorbed becomes connected with 
veins. The inner part of the mesoblast forms the muscles and skeleton, the outer part 
forms the fibrous layer of the skin in which the scales are produced. Eings of bone 
formed round the notochord give rise to the vertebrae, while the bones of the skull 
are formed from the mesoblast round the brain. The formation of the mouth and gills 
takes place after hatching by the development of rods of cartilage between which clefts 
appear placing the anterior part of the intestine in communication with the exterior. 
The mesoblast on each side splits horizontally, its inner thinner layer remaining 
attached to the intestine to form the muscles and fibrous tissue of the gut, while the 
outer part forms the body muscles. The cavity thus formed is the body cavity, and at 
the dorsal part of it are formed the kidneys and reproductive organs. The liver is 
formed as an outgrowth from the intestine. The fins are merely folds of the skin, the 
mesoblast of which gives rise to their muscles and bony rays. 

I have not succeeded in obtaining any specimens of the young sole in process of 
metamorphosis ; the next stage in which I have met with it is that of a small fish 
having in almost all i-espects the same structure as the adult. The smallest specimens 
of this kind which I obtained were from ^ in. to f in. in length (12 to If) mm.). 
One of them is represented in Plate XVI, Fig. 5, magnified 8^ times. The great 

N 



on 

similarity of the young sole at this minute size to the full-grown adult is evident from 
the figure. The chief difference is in the relations of the intestine. The right lateral 
diverticulum of the body cavity is scarcely at all developed, and the four lengths of 
intestine which occupy that diverticulum in the adult are absent. The intestine 
extends backwards only very slightly beyond the anterior ventral interspinous bone. 
The dorsal eye is slightly nearer to the edge of the head than in the adult, otherwise 
the metamorphosis is complete. The colour has disappeared from the lower side, the 
markings of the species are completely developed on the upper side. The pigmentation 
of the upper side is not nearly so dense as in the adult, and the whole body is some- 
what translucent, but nevertheless when the young fish is seen in the living state by 
reflected light, whether resting on the bottom or swimming horizontally in the water, 
its upper side shows the same colour as the adult, and undergoes the same changes of 
colour on different materials in consequence of the action of light. The identification of 
the young sole, Solea vulgaris, at this stage is neither doubtful nor diflJicult, for, although 
some of the characters of the adult are not discernible, others can be perceived easily- 
enough. The large number of anal fin rays distinguishes it from either S. varieijata 
or minuta, while the tubular form of the anterior left nostril distinguishes it from 
lascaris. I obtained specimens of this stage on three occasions within a short time, in 
1889, from the shore at low water at spring tides. On the third occasion I received 
only one specimen which was nearly three-quarters of an inch long (18 mm.). 

I could not trace the further development of these young soles, for they disappeared 
from the shore. But no important changes of structure were required to produce the 
adult, further development consisted almost entirely in the increase of size. For the 
discussion of the later growth reference must be made to the next part of this 
memoir. 

The only other species of Solea whose development I have been able to study is 
S. variegata. The eggs of this species are smaller than those of vulgaris, measuring 
1-28 to 1-36 mm. in diameter. The egg, Plate XVI, Fig. 6, is easily recognised and 
distinguished from that of S. vulgaris by the peculiarity of its oil globules, which, instead 
of being very minute and numerous and aggregated in a number of distinct groups, 
are of considerable size and scattered singly and separatel}'' all over the surface of the 
yolk. The external layer of segmented yolk is present as in *S. vulgaris. The develop- 
ment of course takes place in the same way as in the latter. When the chromatophores 
appear they form another distinguishing feature ; there are both yellow and black 
chromatophores as in vulgaris, but the former are much lighter in this sjjecies, inclining 
to lemon colour, while those of vulgaris are darker. 

Figs. 1 and 2 on Plate X"VT!I show two stages of the hatched larva of the " thick- 
back." The younger. Fig. 1, inuuediately after hatching, has of course the largest 
yolk-sac and the shortest length of body ; it is 2*42 mm. in length. The heart 
is just visible, but is compressed between the yolk and the under side of the throat, 
the pericardium being but slightly developed and scarcely visible. The stage shown 



91 

in Fig. 2 is that of a larva two days after liatcliinp ; the larva from which the figure 
was taken was 2'52 mm. in length. 

The eggs of the other species of Solea I have not yet seen, but for the sake of 
comparison I have illustrated the development of several species of flat-fish. Figs. 
3, 4, 5, Plate X^II, and Fig. 1, Plate XVIII, represent a series of stages in the 
development of the common flounder, Pleuronectes Jlesiis, from the time of hatching 
till the completion of the metamorphosis. Fig. 3, Plate XVII, is from a larva hatched 
under artificial conditions on February 18, 1889, and drawn two days afterwards: 
its length was 3-5G mm. The chromatophores are arranged in such a way as to form 
two transverse bands, one at the level of the anus, the other some distance behind it ; 
two dark bands in these positions are more or less conspicuous in several species of 
Pleuronectes in the adult condition. Fig. 4 shows the same larva when the yolk has 
been entire!}' absorbed and the mouth and gill-slits have been developed : its length was 
3' 94 mm. The pectoral fin is relatively very large at this stage. This condition was 
reached in confinement on February 24, by larvae hatched on February 18. The next 
stage was observed in young fish found in the harbour at Mevagissey at low tide on 
April 2, and is represented in Fig. 5. The length of the fish from which this 
figure was drawn was 10 "5 mm., or a little over three-eighths of an inch. This stage 
is the beginning of the metamorphosis. The left eye has travelled upwards so as to 
project al)Ove the edge of the head, but it is still on the left side. The little fish in 
this condition swims on its edge, but slightly inclined to the left side. It is still 
extremely transparent, so that when alive it is only rendered visible by the metallic 
brilliancy of the choroid coat of the eyes, which shine through the transparent tissues 
in the sun like two metal beads. The yellow spot in the visceral cavity in the figure 
is the gall bladder. Fig. 1, Plate XVIII, shows a later stage in which the left eye 
has reached the edge of the head, so that its lens and cornea are visible on the right 
side. The fish from which this figure was taken was actually smaller than that 
represented in Fig. 5, Plate XVII, probably because its metamorphosis had begun 
somewhat earlier. It seems that in some individuals the metamorpliosis is completed 
while they are smaller in size than others at an earlier stage of development. The 
fish represented in Fig. 1, Plate XVIII, was exactly 1 cm. in length. It was much 
more opaque and more pigmented than the stage previously described ; in fact, though 
slightly translucent when seen under the microscope by transmitted light, to the 
unaided eye it appeared quite opaque. It wiU be noticed that the interval of time 
between the stage of Fig. 4, and that of Fig. 5, Plate XVTI, was about five weeks, and 
that in that time nearly all the organs had reached their final form. The muscles 
and skeleton have developed very greatly. The part of the body behind the anus 
has increased v&vy much in dorso-ventral breadth, and in it the vertebra; with their 
spines, the interspinous bones, and the fin rays have been completely formed. 

Fiw. 2, Plate XVIII, represents the larva of tlie dab (Pleuronectes limanda) imme- 
diatelv after hatching. The larva from which this figure was taken was hatched in 



92 

the Laboratory from an egg artificially fertilised on March 1, 1889. The length 
of the larva was 2"87 mm. The development of chromatophores in the median 
fin fold does not take place in this species at so early a stage as in P. flesus. 

Fig. 3 of the same Plate represents a stage in the development of P. microcephalus, 
the merry sole of the Plymouth fishermen, the lemon sole of Scotland and most parts 
of England. The larva from which this figure was drawn was also hatched in the 
Laboratory, and was four days old ; a small quantity of yolk still remained in the 
body cavity. The chromatophores at this stage form five well-marked interrupted 
transverse bands. 

Fig. 4 of the same Plate represents a larva of the plaice {P. pi atessn), just after the 
complete absorption of the yolk. This larva was also hatched in confinement : it was 
drawn on February 27, five days after hatching. The larva of the plaice is much 
larger than that of any of the other species here mentioned : at the stage figured it was 
6'5 mm. in length. 

Fig. 5 represents the appearance and natural size of a living larva of the brill 
{Rhombus Icevis). The young of the turbot and brill remain pelagic until after the 
completion of the metamorphosis, that is, they swim about near the surface of the 
water, ai\d are commonly met with in the still waters of inlets and liarbours at the 
proper time of year, namely, in June and July. The one here represented was taken 
in Sutton Pool, Plymouth, on June 1. Their pelagic habit is correlated with the 
development of a relatively large air bladder, an organ which is entirely wanting 
in the adult. Although they swim freely in the surface waters they do not swim 
vertically when the right eye has migrated to the left side, but horizontally ; during 
metamorphosis their inclination from the vertical in swimming is proportional to the 
degree of asymmetry of their eyes. 



II 



93 



CHAPTER VTT. 

STRUCTURE OP PHYLLONELLA SOLE.E, VAN BENEDEN AND HESSE, 
A PARASITE OP THE COMMON SOLE. 



On the lower side of the sole are usually found specimens of a small parasitic flat 
worm which lives on the surface of the skin. This creature was first named and 
described by two Belgian zoologists, Van Beneden and Hesse, who called it Phyllonella 
solece. It is of flattened shape, the dorsal surface being slightly more convex than 




Fig. C. 




Fig. C— Egg of Phyllonella solece, seen under microscope in the fresh condition. Magnified 100 times. 
Yig. B.— Phyllonella solew,, the ventral side uppermost, magnified 17 times; p.s., posterior sucker; 
a.g., anterior glandular patches ; p., aperture of penis-sheath ; u., aperture of tlic uterua, 



04 

the ventral, ami the outhne of the body is an oval with projecting ends, so that its 
sliape resembles that of a small leaf. The animal, when adult, is usually about one- 
fourth of an inch in length (6 or 7 mm.), and one-eighth of an inch (3 mm.), in 
greatest breadth, but young individuals are smaller, and larger specimens are often 
seen. The structure of this parasite is shown in the accompanying woodcut, Fig. D, 
which represents the appearance of a living specimen under the microscope. At the 
posterior end of the body is a large muscular sucker, p.s., almost circular in shape : 
the concavity of this sucker is ventral, and it is attached to the body by a peduncle 
at about the middle of its dorsal surface. On the ventral side of the sucker are two 
pairs of hooks imbedded in the skin, with their recur\cd points protruding. One 
])air of these hooks are long and directed backwaixls, their points being near the 
posterior edge of the sucker, the other pair are short, and their points near the centre 
of the sucker. At the anterior end of the body there is a semicircular projection, the 
ventral edges of wliich are provided with a pair of glands, a.(j., for adhesion Behind 
this projection is the small mouth, and at the left hand side of the projection are the 
two genital apertures, /i., ?<., close together. The worm crawls about on the skin of 
the lower side of the sole, anchoring itself to the spines of the fish's scales by means 
of its sucker and its hooks, and using the anterior glands for adhering by that end 
when it moves its posterior sucker from one position to another. 

The most extensive and conspicuous organs are the generative, male and female, 
for the animal is hermaphrodite, and each individual jiroduces both spermatozoa and 
ova. The digestive organs are small, consisting only of a sac-like organ into which 
the mouth opens, and which is lined by very large cells with enormous nuclei. This 
organ may be called the alimentary sac, since it presents no distinction of parts. In 
front of the alimentary sac dorsally are two simple nerve ganglia, giving off a main 
lateral nerve cord on each side, which passes backwards. In the skin above these 
ganglia, ihe cerebral ganglia, are two pairs of eyes, or rather pigment spots which 
are doubtless organs sensitive to light. The renal organs consist of a system of minute 
ramified ciliated tubes communicating with two main lateral tubes, which probably 
open by a single dorsal opening at the posterior end. The rest of the body consists 
of the generative organs, and a dense parenchyma of cells filling up the interspaces 
between the various organs. 

Uniformly scattered throughout the parenchyma of the body are a large number of 
globular organs consisting of aggregations of peculiar cells : these are the yolk-glands. 
They are situated at the ends of the ultimate ramifications of a ramified sj-stem of tubes 
which are the yolk-ducts, and which are completely filled with granular globules similar 
to the contents of the cells of the yolk-glands. The yolk-ducts on each side of the body 
ultimately unite into a single large duct which opens into a sac situated a little to the 
left of the middle line, about one-third of the length of the body from the anterior 
end. This is the j-olk-reservoir : it is elliptical in shape and transversely placed. The 
volk-reservoir is filled with the same material as the volk-diicts ; tlie terminal volk-ducts 



95 

wliich open into it on each side are ventral in position. The ovary is a flattened sac 
with a circular outline situated immediately behind the yolk-reservoir. It is filled with 
small spherical ova, each containing a large nucleus or germinal vesicle. In front of 
the ovary, dorsal to the right main yolk-duct, is a sac with the shape of a pyramid. 
Into this sac or vestibule open a short oviduct from the ovary, a short duct from the 
yolk-reservoir, and two minute short ducts from two spherical capsules containing 
spermatozoa. Here the egg is fertilised. From the vestibule the oviduct is continued 
for some distance as a narrow convoluted tube, which then suddenly expands into a 
thick-waUed sac shaped like a club, the thick end being internal, and the thin end 
opening to the exterior on the edge of the body to the left of the anterior apex. This 
thick-walled sac may be called the uterus. The fertilised ovum in the vestibule is 
surrounded by a quantity of j'olk, and the compound mass thus formed passes down the 
oviduct to the uterus, where it is surrounded by a chitiuous hard shell produced from 
the wall of the uterus The shell has the shape of a triangular pyramid, and its apex 
is prolonged into a long thin filament, swelling at intervals into bead-like globules. 
This filament is doubtless adhesive, and by it the egg when laid, Fig. C, is attached to 
the skin of the sole, there to develop into a young Phyllonella. 

The primary male organs are a pair of globular testes situated a short distance 
behind the ovary, one on each side of the middle line. These testes are simple sacs, 
the walls of which are lined b}' cells which give rise to the spermatozoa. Some of 
these cells become free in the cavity of the testis, and undergo subdivision, each of 
them forming a spherical cluster of small cells, the spermatoblasts, each of which is 
converted into a spermatozoon. From the anterior surface of each testis passes off a 
tube or duct, the vas deferens ; the two ducts unite just behind the ovary, and the 
single vas deferens passes round the left side of the ovarj^ and the left side of the yolk- 
reservoir, dorsal to the left main yolk-duct. In the part of its course which lies in 
contact with the j'olk-reservoir the vas deferens is connected with a coiled sac closed 
at its farther end. This is a reservoir for the ripe spermatozoa, and must be called the 
vesicula seminalis. After a tortuous course the vas deferens opens into an intromittent 
organ, the penis. The mechanism of this organ I have not been able completely 
to elucidate. It consists principally of a club-shaped structure lying between the 
uterus and the alimentary sac. Along its outer half this structure contains a canal, 
which is at the side of it, not in the centre : into this canal the vas deferens opens, 
and by it the spermatic fluid is conveyed to the exterior. The inner half of the 
structure contains granular matter, but, as far as I can make it out, is not a gland. 
At the base of the penis is a pear-shaped structure with radiating bands in its interior, 
which converge into a band apparently of muscle, which seems to run into and become 
merged in the substance of the penis. I am inclined to think that these structures 
have something to do with the protrusion and retraction of the penis, but I am unable 
to understand how they act. 

In the chief features of its structure riiyllonella solece resembles a number of other 



96 



external parasites of fishes -ivhich are classed in a family called the Tristomidfe. 
Most of these forms possess a small sucker on either side of the anterior end of the 
body as well as one large posterior sucker, hence the name of the family. The 
glandular areas described on the anterior end of PhyUonella represent the anterior 
suckers. The Trislomidcc belong to the order Trematoda. 



r.,„ 



Part III. 



BIOJSIOMICAL. 



99 



CHAPTER I. 

GEOGRAPHICAL DISTEIBUTION. 

The common sole is a somewhat southern species. In the neighbourhood of the 
British Islands it is found, in considerable abundance all over the southern part of 
the North Sea, south of a line drawn from Flamborough Head in Yorkshire to the 
north-west coast of Denmark. North of this line it is scarce. It is occasionally taken 
off the mouth of the Firth of Forth, but very rarely. It is said to have been taken in 
the Moray Firth, and off the Orkney and Shetland. Islands. On the east side of the 
North Sea it enters the Baltic, being occasionally taken on the north and east coasts of 
Denmark and the coasts of Schleswig-Holstein and Mecklenburg. Further east in the 
Baltic it has not been observed. Occasional examples have been taken on the west 
coast of Norway up to the sixtj'-fourth degree of north latitude — the neighbourhood of 
Trondhjem. It occurs in some abundance all round the shores of Ireland, and on the 
west coast of Britain from the mouth of the Firth of Clyde southwards, becoming 
more abundant towards the south. It is abundant in the Bristol Channel and 
throughout the English Channel, in the Bay of Biscay and southward along the west 
coast of Portugal. It extends throughout the Mediterranean and probably into the 
Black Sea. How far south the s^^ecies extends along the coast of Africa I have not been 
able to ascertain : it is not mentioned in Lowe's " Synopsis of the Fishes of Madeira," 
1837. 

The other three species, lascaris, variegata, and luiea, are conunon to the south-west 
coast of England and the shores of Italy. In all probability they occur also along all 
the intermediate coast-line. Lascaris occurs also at Madeira, if the specimen called 
lascaris by GUnther is to be considered as of the same species as the English form. 
Solea impar, Bennett, and probably S. niargariii/era, Giinther, both closely allied to 
lascaris, come from the Atlantic coast of northern Africa. 

There are a large number of other species of Solm as here defined besides those 
which occur in Britain. There are several which exist in the Mediterranean, namely, 
Solea Kleinii, Solea ocellata, Solea monochir. One species is known from the west 
coast of Africa, viz., Solea senegalensis. On the west side of the Atlantic the genus 
is but slightly represented. One of the few things in which the citizens of the United 

o 2 



100 



States of America confess that their country is inferior to Europe is that they have 
neitlier the sole nor the turbot in their seas. The only species of Solea on the 
northern part of the Atlantic coast of tlie United States is Solea achirus, Linnaeus, a 
species with no pectoral fins, which grows to the length of only six inches, and is 
quite useless as food. Solea inscripta, Gosse, occurs at Jamaica. Other similar species, 
with pectorals rudimentary or absent, occur at the Keys of Florida. Solea reticulata, 
Gronovii, maculipinnis, mentalis, Jenynsii, in Dr. Giinther's catalogue, are all forms 
witli rudimentary pectorals occurring on the Atlantic coasts of the West Indies 
and South America. In tlie Indian Ocean, according to Dr. Glinther, there is one 
species, Solea Indica, from Madras, also belonging to the subgenus Achirus. In the 
East Indian seas there are several species known: Solea heterorhina, from Celebes 
and Amboyna, and Solea humilis, from the Malacca Straits and Java, with well 
developed pectorals ; Solea trichodactylus and S. Thepassii, with rudimentary 
pectorals. Solea microcephala lives on the coast of New South Wales in Australia; 
further north on the west side of the Pacific we have S. Japonica, from Japan, 
S. ovata, from Chinese seas. On the east side of the Pacific, on the coast of Central 
America, there are Solea scutum, S. Fonsecensis and *S'. fimbriata. Thus the genus is 
well represented in all the tropical seas, extending into the temperate zones both to 
the north and south. But no species is of any importance as human food except the 
Solea vidgaris of Europe. 



K)l 



CHAPTER II. 

HABITS, FOOD, ETC. 

The habits of the adult sole in its natural state cannot be directly observed : we can 
only ascertain the means by which it is captured, the character of the sea-bottom 
whence it is taken, the animals which are taken with it, and the food which is found 
in its stomach. By supplementing the knowledge thus gained with observations on 
the living fish kept in large aquarium tanks we can obtain a tolerably complete 
knowledge of the sole's mode of life. 

The sole is rarely, if ever, captured by any other instrument than the trawl. The 
great majority of the soles brought to market are obtained by the large beam trawl, 
worked by the large deep-sea trawlers, but it is also frequently captured by the 
otter-trawl used chiefly by amateurs, and also by the small trawls used for catching 
shrimps and prawns. The usual depth at which soles are found is from 20 to 
40 fathoms, but it may exist at greater depths ; it probably does not extend beyond 
loo fathoms. 

Adult soles may occur at any depth less than 20 fathoms, but usually in shallow 
water, less than ten fathoms deep, only young individuals are found. However, 
exceptions to this rule occur not infrequently ; the fisherman of tlie Plymouth 
Laboratory has several times caught an adult sole in Plymouth Sound within the 
Breakwater. Once he caught a full-grown specimen of large size in the Catwater, 
which is the estuary of the Eiver Plym, opening into the north-east corner of the 
Sound. On May 9, 1889, he took a specimen 13f in. (35 cm.) long, a short dist.ance 
from the mouth of the same estuary, and a third specimen he captured a little later 
in another part of the Sound. Small specimens six and a half to nine and a lialf 
inches (17 to 23 cm.) in length are not unconnnon in the Sound, half a dozen being 
frequently taken in two or three hours' work with the shrimp trawl. These immature 
soles in fact, according to ray experience, are more abundant within the Sound than on 
the neighbouring open shores outside it. 

Off Plymouth soles are comparatively scarce at the present time : it is rare to take 
more than four or five in a single haul of the trawl, and sometimes only one or none 
at all are obtained. At a considerable distance south of the Eddystone they become 



102 

somewhat nidie plentiful. They are much more abundant on a rough area of ground 
to the west of the Eddystone, off Dodman Point in Cornwall. In this neighljourhood 
I saw about fifteen soles in a single haul of the trawl in April, 1889. This ground 
is often called the " California " ground, a name which was given to it when it was 
first worked at the time of the rush to the gold-diggings in California. On the area 
calhid by the Plymouth fishermen the Mount's Bay ground, soles are fairly abundant. 
This ground lies off the entrance of Mount's Baj' to the south of the Wolf Rock. 
When I was on a trawler woiking there in April, 1889, the catches of soles numbered 
six, seventeen, and fifty-seven, in three did'erent hauls. The species is still more 
abundant on the fishing grounds off the north coast of Cornwall, and in 1889 large 
numbers of trawlers from Ijowestoft, Grimsl)y, and other ports on the east coast 
worked over these grounds for several months in the earlier part of the year ; but 
I have i^ever been there myself. In 1889 the Newlyn fishermen, who are usually 
exclusively engaged in drift-net fishing, found that large soles were abundant inside 
Mount's Bay on the west of the Land's End promontory. They obtained small 
trawls about twenty feet long which they worked over this area from their small 
luggers in the month of Marcli, when no mackerel or other surface fish were to be 
caught. One boat in which I went out obtained eleven, seventeen, and eleven soles 
in three separate hauls, many of the fish being very fine specimens. 

None of the grounds mentioned are at a much greater depth than forty fathoms ; 
over the ground last mentioned the ground varies from twenty to thirty-five fathoms. 
All these areas are more or less sandy, the sand being in all cases of a very fine 
texture and of didl grey colour. Trawls cannot be worked over a hard and rugged 
bottom formed of rocks, but some of the grounds above mentioned where trawling is 
carried on are by no means smooth. From the California ground the trawl brings 
up numbers of the large nmssel-like bivalve. Pinna nohilis, called caperlonga at 
Plymouth, numbers of Pectens, called at Plymouth queens, at other places scallops or 
clams, and large rugged stones. But we may conclude from the habits of the sole in 
the aquarium that such ground contains patches of loose sand or gravel, and that 
the soles live on these ; for in the a([uarium the sole invariably when alarmed, like 
all otlier flat-fish, buiies itself in sand or gravel by rapidly shaking its longitudinal 
iins. If a live sole in caijtivity is placed in sea water on a smooth solid surface, such 
as the bottom of a flat porcelain dish, or the bare wooden or slate bottom of a tub 
or tank it instinctively shakes its fin in the peculiar way by which it shakes the sand 
or gravel over its "back." when there is any sand or gravel beneath it. This rapid 
movement of the fins is therefore a characteristic of its habits of life, and it is extremely 
effective. The fish on a layer of sand, when alarmed, disappears in an instant, the 
agitation of the sand renders the water around it turbid so that it is diflicult to 
locate the exact spot where the fish has buried itself. Usually when resting undisturbed 
beneath the sand or gravel it leaves its eyes uncovered, and these can be detected by 
careful search : but not easily for they do not differ greatly in appearance from small 



103 

bright pebbles or fragments of ttoue. When the material the fish rests ou is fine, like 
sand, or contains an admixture of tine particles, a thin layer of the finer material 
remains on the back of the fish when it emerges and moves about ; the fine particle 
are retained on the skin partly by the adhesive property of the viscid mucus which 
exists on the skin of all fishes, and partly by the minute spines of the scales The 
sole thus moving gently about with its upper side covered with sand is partially 
concealed, often only its actual movement betrays its existence. 

Solea lascaris is a rare fish in the neighbourhood of Plymouth. For a long time 1 
never met with a single specimen. The fishermen did not seem to know it by any of 
the vernacular names given in books. The first specimen I obtained was discovered 
by the Laboratory fisherman among a number of common soles exposed on the fisli 
quay for auction. He selected it on account of its peculiar appearance, after I had 
described the species to him and requested him to search for specimens. The 
fisherman to whom it belonged when asked its name said it was a " sand-sole." I 
could not ascertain accurately where this specimen was taken, but it probably was 
caught a long distance from land towards the central region of the channel. On 
June 17, 1889,1 trawled at night in Whitsand Bay for the purpose of obtaining if 
possible young specimens of the common sole. In the products of this trawling I 
discovered on my return three small specimens of Solea lascaris measuring 7^, 7^, 
6f inches (19 cm., 19 cm., 17 cm.), respectively. The depth of water where these 
were taken was three to five fatlioms, the bottom a fine clean sand of liii-ht vellow, 
almost silvery, colour. 

Solea variegata, the thickback, is very common off' Plymouth, but only in deep 
water. I have never met with a specimen in or near the Sound, either young or 
adult. On April 19, 1889, when I was on board a trawler fifteen or sixteen miles 
S.W. of the Eddystone, 213 thickbacks were taken in a single haul of the trawl. On 
the Mount's Bay ground the}- are much less plentiful. 

Half-grown specimens of Solea lutea are fairly common in Plymouth Sound, but I have 
never found adults there. The only adults I have seen were obtained from deep 
water by a larger trawl, and the exact locality was not recorded. In the Sound the 
young sjjecimens, one to two inches in length, are especially abundant in Cawsaud Bay, 
in three to five fathoms of water on a bottom of fine sand of a dull grey colour. I have 
frequently taken half a dozen there in a single haul of the shrimp trawl, together witli 
young scald-backs [Arnoglossus laterna). The shrimp trawlers believe i)oth these fish to 
be the young of the common sole. 

I have not been able to keep thickbacks alive in the acpiarium, but there are living 
specimens of the lascaris and lutea in our tanks, and they do not differ in their habits 
from the common sole. 

There is no doubt, then, that the common sole lives naturally on ground consisting of 
sand or gravel or other loose material, and that it has the instinct of seeking 
concealment bv burvinrr itself beiieatli the surface of the ground by a rapid shaking of 



1()4 

its fins, an instinct which is exercised at tlie least cause of alarm, as the fish is 
exceedingly shy and timid. All the other flat-fishes have the same habit, but of those 
observed in our aquaria, namely, the plaice, dab, flounder, and turbot, none remain 
concealed so persistently as the sole, at least in the daytime. In the night soles 
behave quite differently, they then emerge from beneath the ground and move actively 
about in search of food. In the daytime it is extremely difficult to discover how 
many soles there are in a given tank even by driving them out of the gravel with a 
stick : but on going to the same tank iu the dark with a lighted taper one may count 
twenty or thirty where only five or six were expected. But they soon disappear if the 
light is held over the surface of the water. 

The sole then is a nocturnal fish in the aquarium, and therefore doubtless also at the 
bottom of the sea. This agrees with the belief of the majority of trawlermen that 
more soles are caught in the trawl by night than by day. I have met one or two 
fishermen who deny this and assert that they have sometimes taken a good number of 
soles in a daylight haul and scarcely any in the following night. But of course 
exceptional cases may well occur, and are probably to be explained by the fact that 
soles were abundant in the track passed over by the trawl in the daytime, and very 
scarce in the ground swept at night. Of course some soles are taken in daylight, and 
it will be easily luiderstood when the mode in which the trawl works is considered, 
that it depends on the position and behaviour of oarh individual sole whether it passes 
over the foot-rope into the net or not. If the foot-rope is heav}' and the trawl going 
at a moderate speed it may disturb the ground deep enough to cause naost of the soles 
in its i)ath to rise from the bottom, in which case they will most likely pass over the 
foot-rope and be swept into the net : if on the other hand the foot-rope 2)asses more 
lightly over the surface, or if the soles bury themselves more deeply instead of rising 
in alarm the rope will pass above them and they will escape capture. 

There can be no doubt that at 30 to 40 fathoms depth beneath the surface of the 
sea there is in the da3'time a good deal of light, but still much less than at the surface 
or in an aquarium tank. It has been ascertained that light disapjiears altogether at 
200 fathoms, and if we assume that the absorption is proportional to the depth there 
must be at 50 fathoms three-quarters of the quantity of light that exists at the surface. 
Now the quantity of light in our aquarium is a great deal less tiiaii the quantity 
outside, as a great part of the windows are obscured. It follows, therefore, that the 
tanks in the aquarium are not very much more illuminated than the sea bottom at a 
de})th of thirty fathoms, ai\d it may justly be concluded that soles in their natural 
condition at that depth will for the most part remain buried during the day and emerge 
from the sand to seek food at night : the sole therefore is a nocturnal fish in its natural 
state. 



105 



The Food of the Sole, and its Method of Feeding. 

Although the sole is more active by night than by day, it can often be seen feedin. 
m our tanks nx the daytnne : there is not a constant supply of food in the tanks, anS 
when food xs thrown .n the fishes are usually so hungry that they begin to fe^d at 
once. The food snpphed to the soles and other flat-fishes consists principally of marine 
worms chxefly Nere^s Dumerilii), shrimps, and fish cut up into small pieces, usually 
pilchard, mackerel, or gurnard. Of these the soles prefer the worms. In seeking their 
food the soles are guided first of all by the sense of smell : by this they perceive the 
presence of food in thexr neighbourhood, and the sense of sight is not employed 
for this piirpose. But in hunting for their food, and in localising its position before 
bitmg at It, they rely entirely on the specialised tactile filaments of the skin on the 
under side of the head. A sole when searching for food moves slowly about <.ently 
tapping every part of the sandy bottom with the lower surface of its head While 
the sole is thus engaged its back is very frequently covered with a thin layer of 
sand, so that scarcely any part of it is visible except the eyes and mouth and some 
of the filaments below the snout when the latter is raised : it is only noticeable on 
account of Its movements, and because its form can be traced out and distin<nii.hed 
from tlie flat surface of the sand around it, When in the course of this defiberate 
exploration the lower side of the head feels a worm or other morsel of food the sole 
immediately seizes it with a vigorous and sudden snap of the lower half of'the jaws 
where the teeth are situated, and then swallows it with the sand which adheres to it 
I have often placed a worm on the upper side of a sole thus engaged in hunting its 
prey. When this is done it makes not the shghtest diff^erence to the sole's behaviour • 
the fish goes on tapping as before, evidently unconscious that it is carryin^r a palatable 
morsel about with it. When the sole feels a worm or other piece of food with its 
tactile filaments it cannot see it, and it never snaps at any food which it has not first 
felt in this way. It is in fact unable to localise the position of its food and so to 
direct the motion of its jaws to the object to be seized unless it has felt this object with 
these tactile filaments. In other words the afferent sensory impulse produced by the 
contact of the food with the sensitive filaments is necessary for the co-ordination of the 
movements of the head and jaws by which the food is seized. 

I have examined the intestines of a large number of soles in order to discover what 
they had been feeding on before they were caught. It is the custom of trawlers to gut 
their soles on board before they put them away in the hold of the vessel. They also 
gut turbot, brill, dorey, and haddock, though of the latter they do not usually 'catch 
many ofi" Plymouth ; sometimes they take a considerable number ofi' Mount's Bay and 
the north coast of Cornwall. I obtained the intestines of soles sometimes by puttincr 
tliem into a jar of spirit when I was out with a trawler myself, more frequently by 
sending jars of spirit on board a boat and paying tlie men to bring back in them the 



106 

intestines of all the soles they caught. It is very seldom that anything is found in the 
stomach or intestine of a sole which can be satisfactorily identified. The stomach is 
very slightly differentiated, it is only distinguished by the somewhat greater thickness 
of its walls from the intestine, and is only marked off from the latter by a slight 
pyloric constriction situated beneath the middle of the liver. The stomach after death 
is almost invariably found empty. In the course of the intestine in a small percentage 
of specimens small masses of the indigestible remnants of food occur. These masses 
are usually black and enveloped in mucus. Usually they contain fragments of shells 
with bristles of marine (Clia3topod) worms and other debris, and rarely something is 
found in them whose specific origin can be recognised. The following is the record of 
the intestines I have examined : — 

December 22 and 23, 1887, 9 miles W. by S. of Eddystone, 40 fms. A number of 
specimens : six contained food. 
(1.) Proboscis of Gasteropod, one small Ophiurid, pieces of Lamellibranch shells. 
(2.) Pieces of Lamellibranch shells, and remains of the contained animals. 
(3.) Fragments of Lamellibranch shells. 
(4.) Ditto. 
(5.) Ditto, and a long specimen of errant Polychaste worm, genus and species 

unrecognizable. 
(G.) Fragments of Lamellibranch shells. 

January 23, 1888. Nine miles S.W. of Eddystone, nine specimens, two containing 
food. 
(1.) i\'ika edulis, Risso (a Decapod Crustacean) a single specimen; also a Holo- 

thurian, sp. ? 
(2.) llemains of Chaetopoda. 

Same date. Six miles S. of Eddystone, sixteen specimens, all empty except one. 
(1.) A piece of Serhdai'ella (Hydroid). 

January 30, 1888. Kine miles S.E. of Eddystone; bottom sand. Fourteen 
specimens, three containing food : — 
(1.) Two Synapta digitata. 
(2.) Several OjdiiiKjhipka albida. 
(3.) Two Ophioglt/pha albida. 

February 7, 1888. Seven or eight miles W. by S. of Eddystone; "queen ground," 
i.e., Pecten opercidaris abundant on the bottom ; nine specimens, four con- 
taining food. 
(1.) Nine Ophioglypha albida; one Chtetopod unrecognizable. 
(2.) One Chajtopod. 

(3.) Two Ophiogh/p/ut albida, one Amphipod. 
(4.) Four Oj'liioglgp/ta albida, one Amphipod. 



II 



107 

February 17, 1888. Twenty-five miles off the Lizard, 40 fms., sand. A great 
number of specimens, eight containing food. 
(1.) Eemains of Ophioghjpha alhicla, and fragments of Lamellibranch shells. 
(2.) Fragments of Lamellibranch shells. 
(3.) A few fragments of shells, small pieces of membrane, and a large number of 

large Chtetopod bristles, Aphrodite or Hermione. 
(4.) Small Lamellibranch shells and fragments. One of these close to the anus 

was entire, the colour unaltered and the animal undigested. 
(5.) SmaU LamelUbranch shells and bristles oi Aphrodite or Hermione. 
(6.) Fragments of shells ; one small Lamellibranch Donax shell entire near 

anus, animal absent. 
(7.) Chastopod bristles. 

March 24. Off Mount's Bay. Thirty-seven specimens, ten containing food. 
(1.) Pieces of Sertularian Hydroid, and remains of Chfetopod tube. 
(2.) Anterior part of large Chsetopod of fam. Terebellidse. Fragments of shells. 

Piece of CcUaria fistulosa. 
(3.) Fragments of shells. Piece of Chastopod tube. 
(4.) Large Chsetopod bristles, probably of Hermione. 
(5.) Piece of Chastopod tube. Fragments of shells 
(6.) Large bristles, probably of Hermione. 
(7.) Piece of Chastopod tube. Fragments of shells. 
(8.) Fragments of shells. 
f9.) Large bristles, probably of Hermione. 
(10.) Tail of Decapod Crustacean, probably shrimp. 

April, 1889. Off Mount's Bay. A large number of specimens. 
(1.) Bristles of CliEetopoda. 
(2.) Bristles of Chsetopoda, among them the dorsal hook of Melinna cristata, 

Malmgren. 
(3.) Cuticle of a long specimen oi Linnbrinereis sp. 
(4.) A long, much-digested specimen of a Gephyrean, Sipvnculus (?) 

Also in several the aciculi of Hermione or Aphrodite and, in several, 
cyhndrical masses of debris containing small shells, e.g., Pecten tigrinus and 
fragments of shells, entangled fibres, and pieces of membrane from the tubes 
of tubicolous Chsetopoda ; also fragment of calcareous Polyzoon. 

I believe that the fragments of shells and pieces of tough membrane which occur so 
frequently in the sole's intestines are the remains of the tubes of Thelepus circiumita, 
Malmgren, a Chsetopod belonging to the family TerebcllidiB, which inhabits a mem- 
branous tube attached by its whole length to stones or shells, and covered externally 
with calcareous fragments of all kinds, such as fragments of shells, or entire small 

p 2 



108 

shells, small stones, pieces of calcareous Polj'zoa, &c. If this is so, this species and 
others possessing a similar tube must form a large portion of the sole's food. The 
total number of specimens the contents of whose stomachs are recorded in the above 
list is thirty-six. Of these eighteen, or 50 per cent., contained remains of marine 
annelids (Chajtopods). If we add to these the number of specimens which contained 
no remains of Cha;topods but fragments of shells, probably derived from the tubes 
of annelids, the number becomes twenty-eight or 77 per cent. Seven specimens 
contained Ojihiogli/pha albida or other Ophiurid, or 19 per cent. One specimen 
contained Synapta difjitata, and one another Holothurian. Crustacea were present in 
four specimens, or 1 1 per cent. In tliree specimens there were Mollusca probably 
not derived from the tubes of Chietopods, or over 8 per cent. Thus it is evident 
that soles in their natural state feed chiefly on Chietopods, and it is probable that the 
bodies of these are rapidly digested, so that it is very diflicult to identify the species to 
which their remains belonged. 



o 



Parasites. 

The common sole is remarkably free from parasites, which in many fishes occur 
constantly in great number and variety. I have seen no internal parasites in the sole 
except an occasional Nematode, or small thread-worm. Of external parasites the only 
form I have observed is the Trematode, PhjlloneUa solece, whose structure has been 
described at length in the preceding Section. This creature appears to do no harm to 
the fish. I have never seen any signs of irritation or inflammation of the skin on which 
numbers of the parasite were hving. Sometimes as many as twenty or thirty specimens 
of the parasite occur on a single sole. Phyllonella is, as I have described it previously, 
hermaphrodite, but it does not fertilise its own eggs. I have not seen it in copula- 
tion, but it may be inferred from the structure of the generative organs that two indi- 
viduals copulate reciprocall}% the penis of each being inserted into the uterus of the 
other, and the seminal fluid received by each uterus passing up the oviduct to be 
stored up in the spermathecas. Fertilisation of the ova then takes place after copu- 
lation, and is efiected by the spermatozoa which are expelled from the spermatheca3 
into the vestibule into which the ova pass from the ovary. The fertilised ovum, 
together with a quantity of yolk, is surrounded by its peculiar shell in the uterus and 
then the deposited ovum adheres by its filament to the skin of tlie sole. I have not 
traced the development of the parasite, but have no doubt that it is direct, that the 
young is hatched in a form closely resembling the adult, and immediately adhei'es by 
its posterior sucker to the sole's skin. The parasite doubtless is nourished by the 
mucus of the skin on which it lives, but how far its nutrition is efiected by digestion of 
the mucus within the small alimentary sac, and how far by direct absorption through 
the surface of the body, it is impossible to say. The parasites spread from one sole to 
another in all probability when the fish accidentally come into contact with one 
another. 



109 



Enemies. 



I am inclined to think that the principal and most deadly enemy of the sole is man. 
But my evidence on this subject is by no means extensive. I have never seen an adult 
sole in the stomach of any fish except the angler, but on the other hand, I have not 
devoted much time to recording the contents of the stomachs of the larger predatory 
fishes. Considering the great timidity of the sole it is difficult to avoid the inference 
that it has many enemies to fear. Probably young soles aud other flat-fishes living in 
the conditions in which I found them in Mevagissey harbour are largely devoured by 
gulls and shore birds when left by the receding tide in the shallow pools of the shore, 
but I cannot assert this from direct observation. I have once or twice seen larse 
conger seize and devour flounders in a large tank of our aquarium ; there were no 
soles in the same tank, but it may be inferred that conger would devour soles when 
they had the opportunity, and that they do devour them in the open sea. But it 
must be mentioned that our captive conger have by no means eaten all the flounders 
in their tank ; probably they are never so hungry when fed regularly in captivity as 
when they have to seek their own living in the wild state, and therefore conger may 
reasonably be reckoned, ou the south coast, among the enemies of the sole. I have 
never teeii the common spotted dog-fish [ScyUium canicula and So. caiulus) eat flat- 
fishes in the tanks, though they are kept together in the same tank, but I think 
cod and hake probably eat soles and other flat-fishes sometimes. One of the 
commonest and most destructive enemies of ground fishes is the angler {Lophius 
piscatorius) which grows to an enormous size and consists almost entirely of a huge 
mouth and a small conical tail. I have frequently seen several large specimens of 
this fish in a single haul of the trawl, and it constantly swallows other fish, including 
flat-fish, even after it is in the trawl, its voracity being so great that it devours its 
fellow captives. I have often seen soles taken from its stomach on the deck of a 
trawler, and when extracted thej' are usually quite uninjured and are packed away 
with the rest for market ; so that when we eat a sole we cannot be certain that it has 
not been swallowed before. The angler is very inactive, its powers of locomotion 
being limited. It partly buries itself in the sand on which it lives, and its colour and 
appendages are such that in this condition its true character is perfectly concealed. 
Over the head are long flexible filaments which are sxipposed to serve as a lure to 
attract other fishes, but which probably have little eflect on soles because they do 
not hunt by sight. The angler thus forms a living and deadly pitfall. Any fish 
coming unconsciously near its terrible gape is seized and engulphed in the great 
cavity of its mouth, and soles of the largest size are swallowed by it with ease. 



110 



CHAPTER in. 

COLOUE. 

The colour and markings of the upper side of the common sole, so far as they are 
permanent and characteristic of the species, have already been described. But, as was 
mentioned in connection with that description, the skin of the fish is capable during life of 
exhibiting considerable changes in the intensity and to some extent in the quality of its 
colours. It is exceedingly difficult to study these changes of colour in a living fish if the 
material on which it is placed consists of fine particles, like sand or mud. For the fish 
will persist in burying itself, and it is impossible to keep the skin free from particles of 
ihe material, so that an accurate estimation of the colour under particular conditions 
can scarcely be made. It is not difficult to keep a sole alive and in a healthy condition 
for several days or even weeks in a shallow vessel supplied with a current of sea water. 
In order to study the colour-changes carefully I kept specimens in this way, allowing 
them to rest either on a solid surface or on a material of coarse texture without fine 
particles, namely, coarse gravel or broken coal thoroughly washed in running water. 

It is generally believed that the colour and marking of the sole's skin assimilates 
itself to the colour and texture of the ground on which it rests. The following 
observations were made in order to obtain definite results as to the extent and 
character of this assimilation : I found that the contrast between the markings and 
the ground-colour of the skin was most conspicuous when the fish was lying on a coarse 
bright clean gravel. The gravel which I used had a general orange tint, but it 
contained, besides yellow and orange coloured pebbles, a considerable number of black 
and white. The appearance of the fish when resting on this gravel is shown in Plate I. 
The ground colour is a greenish grey, and on this ground all the spots and markings 
ever present in a sole are well marked. The principal dark blotches are very 
conspicuous and well defined ; the irregular lighter bands which connect them ramify 
in the spaces between them. The blotches are in places quite black, the black being 
always confined to the outer part of the scales, the anterior part of these being always 
somewhat lighter. The small white spots alternating with the blotches are also fully 
expressed. The dark spot at the outer end of the pectoral is pronounced. It is 
evident from the drawing that there is no exact similarity between the colour and 
markings of the fish and the appearance of the surrounding gravel ; but it is also 



Ill 

evident that the sole in this condition has, like the gravel, a variegated colouring 
which at some distance from the eye renders it less conspicuous. The black spots and 
the small white spots resemble the black and white pebbles of the gravel ; but on the 
other hand, the continuous streak of opaque white along the edge of the fins is 
distinctly conspicuous. A sole on gravel of this kind in a tank of some size is usually 
either completely or partially buried under the gravel, and when the fins are thus 
concealed and only part of the body exposed the sole may easily escape notice from a 
human observer. On the other hand, it is also very easy to discover a sole in such a 
condition when one looks for it. I believe that soles are seldom on gravel in their 
natural state ; for I have found that on gravel or sharp sand they nearly always sooner 
or later injure their fins or skin, and that abrasions so produced usually lead to 
inflammation which causes death. 

I placed another sole in a large shallow dish of white porcelain of the kind used in 
photographic manipulation. No material of any kind was placed in the dish, the fish 
rested on the smooth white surface of the porcelain, and it was exposed to the full 
daylight of the south windows of the Laboratory. Plate III is a reproduction of the 
water colour drawing made from the sole in this condition. The paleness of the 
colouring is extraordinary. The darkest tint in the blotches is a straw colour, 
scarcely darker than the yellow of the fin-membranes. The ground-colour is a pale 
grej' with a slight tinge of blue in places. The white spots have disappeared entirely, 
a result which would not have been expected : the spots whei'e they existed are 
somewhat blue. The dark spot on the fin is the darkest colour in the whole surface, 
and has still streaks of dark brown between the fin raj^s. The sole used in this 
experiment was a male 10^ inches (26"7 cm.) long ; but I found that the sole from 
which Plate I was drawn became as pale as this when placed under the same 
conditions. 

The drawing of the sole just described was finished on June 8, 1889. This sole 
died shortly afterwards and its appearance the day after death is represented on PI. IV. 
Another sole was taken for the drawing given in PL I. I found when this latter 
specimen was placed on the white porcelain that it became in a few minutes as light 
as the figure on PI. Ill, but after it had been left all night in the same condition, on 
the following morning the small spots which on gravel were opaque white had become 
quite a dark grey and formed a marked contrast to the surrounding yellow. 

To ascertain the maximum darkening of colour possible I used the same sole from 
which PI. I was taken. At first I found it difficult to produce any colouring much 
darker than that of PI. I. I lined the porcelain dish with black paper and placed the 
fish on that, but it showed much the same colours. Then I varnished the dish with 
black varnish of a deeper black than the paper, but got no better result. It then 
occurred to me that the maximum of darkness could not be obtauied until the quantity 
of light was reduced ; accordingly 1 placed some washed coal at the bottom of a tub 
about nine inches deep, and placed the sole on this ; then I placed the tub on the 



112 

north side of the Laboratory at some distance from the windows in a position where it 
was partly shaded. Then the result shown in I'hite 11 was produced. But the 
drawing for this plate had to be finished from the sole in the position I have described. 
When the sole in the tub at its maximum darkness was carried to a table in front of 
the window, the colours immediately began to get lighter. I found that the white 
spots were exceedingly curious in their behaviour. As I have mentioned, on white 
])orcelain with plenty of light the white spots disappear as such and are changed into 
bluish spots which sometimes become quite dark and conspicuous. The white spots 
also disappeared in the sole which was kept on coal with very little light, reappearing 
in a few seconds when more light was admitted. Thus the white spots are generally 
visible except on white ground with a great deal of light, or black ground with very 
little. 

As to the rate of change it is usually quite rapid. A sole placed on the white dish 
begins to get lighter almost immediately ; when it is disturbed with the hand the colours 
become darker again, but when left alone it continues to grow paler, However, the 
full effect is not seen till the fish has been some hours on the white ground. 

A sole kept on coarse yellow gravel in front of a window is very inconstant in its 
colouring : it sometimes exhibits its markings quite distinctly for some hours, and then 
begins to grow pale, its black blotches almost vanishing. 

On May 22, I took a sole in Avhich the markings were well expressed and the 
colour moderately dark, and placed it on the white porcelain dish ; in a short time the 
colours had become pale, and the dark blotches had become yellow. Then I ])laced 
some fine shingle in the dish, intending to bring the niarkings out again, but to my 
surprise the black blotches had not returned when I examined the fish the next 
morning, and did not return completely when I placed it in an oaken tub nine inches 
high, although the ground colour became somewhat darker. 

All the changes are evidently due to the action of light and depend on the quantity 
of light acting on the sole, not on the tint or texture of the ground on which it rests. 
The behaviour of the whjte spots I cannot 'yet explain, but all the rest seems to me 
easily intelligible when regarded in this way. The colour and markings of the skin are 
due to a vast number of chromatophores situated in the skin beneath the epidermis: 
these are of two colqurs, the black and the yellow, and in some places there are others 
containing a somewhat iridescent pigment. The last are particularly abundant in the 
white spots, the black especially abundant in the dark markings. Light causes these 
chromatophores to contract. Whpn expanded the chromatophores or pigment-cells 
are stellate, giving out ramified processes on all sides. When they are contracted all 
these processes are withdrawn and each cell becomes a mere minute speck of pigment 
The position of these chromatophores is fixed, and therefore when they are expanded, 
in the absence of light, the markings always reappear in exactly the same positions, in 
fact the markings never entirely disappear. When a very strong light falls upon the 
sole all the chromatophores are contracted, and all the parts become proportionally 



113 

lighter; when the light is diminished the chromatophores expand and the colours 
become darker. It is evident that with the same amount of illumination the alteration 
of the colour and composition of the ground on which the sole rests alters the quantity 
of light acting un the fish. For if the ground is black all the light whicli falls upon 
that ground is absorbed, and the sole is only affected by the rays which fall directly 
upon it, while if the ground is light-coloured nearly all the light which falls upon it is 
reflected, and the diffused light which falls upon the sole is therefore greatly increased. 
Just as a room is n\uch lighter with the same windows if its walls are white than if 
they are black. 

The sole does not become uniformly coloured on a uniformly coloured ground. In 
some of the laboratory tanks we have at the bottom a dark grey fine sand brought 
from a part of the sea shore. This sand is extremely uniform in colour, and is exactly 
of the same kind as the sand brought up by the trawl from the trawling grounds ofl' 
Plymouth and off Mount's Baj^. In the tanks the soles usually have some of this sand 
on their skins, and are therefore by no means conspicuous, but whenever their skins 
are visible it is seen that the black markings are pronounced. The ground colour of 
the soles in this condition approximates closely to that of the sand, but the presence of 
the black spots does not seem to me to aid in the resemblance at all. I placed a large 
sole in a shallow tub on some of this sand in order to make a careful observation. 
After three davs the colouring of this sole was as follows : The intermediate black spots 
were almost invisible ; of the dorsal series the second was faint, the third, fourth, and 
fifth well marked and black ; of the median series only the third and fourth were 
well marked, but not black. The ventral spots were all visible but faint ; termination 
of the pectoral reddish-brown, white spots alternating with black quite distinct. 



114 



CHAPTER IV. 

BEEEDIXG. 

The egg of any particular species of fish is derived from a female individual of that 
species, and after a process of development becomes another individual of that species, 
presenting the characteristic specific characters. As the eggs of nearly all marine fishes 
are left to themselves after being shed from the body of the female, the parents taking 
no care of them, there are only two possible methods of ascertaining the species to 
which a particular kind of egg belongs, or of tracing the development of any particular 
species of fish. One method is to observe the deposition of the eggs by the female, or 
to detain them by artificial fertilisation, then to examine these eggs and study their 
development. The other is to examine all kinds of eggs that can be obtained, and to 
trace their development up to the stage when the young fish presents specific charac- 
ters by which it can be identified. The latter method presents more difficulties and 
uncertainties than the former. 

The greater number of marine fishes shed eggs or spawn at one particular period of 
the year, a period extending over one or a few months. During the rest of the year 
the development of ova in the ovaries proceeds gradually until the next annual breeding 
season, when the annual crop of mature ova is again shed. As the ova develop in the 
ovary they increase greatly in size and number, and thus the ovary itself becomes 
much enlarged, and finally attains a very considerable size in proportion to the rest of 
the body of the female. This enlargement of the ovary produces a corresponding 
enlargement of the visceral region of the female. The small testes do not exhibit any 
corresponding increase in size in the sole. In most fishes the testes in the male enlarge 
at the breeding season in some degree, and in some they become very nearly as large 
as the ovaries in the female. In the herring, for instance, it is not possible to distinguish 
the males from the females among ripe specimens taken from the net when captured, 
except by squeezing them and observing whether eggs or milt escape from tlie genital 
aperture. But in the sole the ripe females can be easily distinguished by the enlarge- 
ment of the ovarian region. It is not so easy to distinguish the smaller males from 
small immature females, but among larger specimens the males can usually be identi- 
fied by holding the fish up against the light, when in the male the posterior part of the 
ventral region behind the intestines is seen to be translucent ; while in the female even 



115 

if the ovary Le not mucli enlarged it usuall}' j^roduces an oi)acity extending back far 
behind the intestines near to the base of the taih 

The enlargement of the ovaries in the female sole becomes noticeable in January and 
February, and ripe actively moving spermatozoa ai-e found at this season by examining 
under the microscope a portion of the testis of the male. I have not succeeded in 
observing the natural deposition of the ova by living soles in captivity. I attempted 
to do this in the spring of the present year (1889). At my request living soles were 
brought to the aquarium during the previous vrinter months from the deep sea 
trawlers and from the shrimp trawls worked in Plymouth Sound. But the specimens 
obtained from the latter were all small, and although they lived well were too young 
to breed ; while the larger ones from the large trawlers although living when brought 
in invariably died after a. few days in the tanks. The reason of this was that the large 
soles were always more or less injured by the trawl or by subsequent handling. The 
large trawls are towed usually for a long time, six to twelve hours or more, and the 
captured soles and other fish during this time are injured by their struggles and by the 
pressure and weight of the whole contents of the trawl. After the soles are placed in 
tubs of water on board the vessel the voyage back to harbour occupies a long time 
during which they are knocked about by the motion of the vessel. In consequence of 
this mechanical violence the skins of soles brought to me from the deep sea were 
always more or less abraded, and the scales torn off at one or more places. The 
injured parts of the skin in a few days always underwent inflammation and sloughing, 
and the diseased condition spread over the surface till the fish died. I have found 
that the sole is tenacious of life and will bear a great deal of handling so long as the 
skin is uninjured and the scales not removed, but that very slight injury to the skin 
and scales leads to inflammation and death. In other fish, for instance, the conger and 
grey muUet {Mugil chelo), considerable wounds on the skin are healed up in a very 
short time without any inflammation ; the muUet will reproduce nearly aU its scales m 
a week or two. 

I was unable therefore to study the breeding of the sole in specimens living in 
captivity, and my investigations of the reproduction of this species, as of many others, 
have been carried on at sea on board of trawhng smacks by examination of the fish 
when brought up by the trawl. 

With very few exceptions the eggs of all deep sea food-fishes have been found to be 
small in size, spherical in shape, transparent, and buoyant in sea water, and after being 
extruded by the parent fish to undergo development while suspended, separate and 
independent of one another, in the surface waters of the sea. All the flat-fishes 
investigated have been found to shed eggs of this kind, and the sole proves to agree in 
this respect with its allies, the plaice, flounder, turbot, &c. As in other fishes, gentle 
pressure by the fingers and thumb applied to the ovarian region of the ripe female 
sole causes the ripe ova to escape from the aperture bj^ which the ovaries open to the 
exterior. The ovaries lie entirely behind the aperture, and therefore the pressure must 

Q 2 



IIG 

be exerted from behind forwards. To examine the eggs and keep them alive they must 
be received when pressed from the fish into a bottle of clean sea water. By squeezing 
a number of captured soles in this way in March, when the ovaries are found to be 
much enlarged and soft to the touch, some are found from which transparent eggs can 
be pressed out. When a considerable pressure is exerted part of the contents of the 
ovary can be squeezed out of any sole in which the ovaries are large, but when the 
ripe transparent ova have once been obtained it is easy to distinguish them from the 
.smaller unripe ova w^hich escape when too much pressure is applied. These unripe ova 
are yellowish-wliite and quite opaque : they do not separate from one another when 
they fall into sea water, and membranes containing blood, derived from the tissues of 
the ovary, are usually seen connected with them. In March a number of soles taken 
at one haul of the trawl include, besides somewhat small immature specimens and males, 
some large females which yield no ripe eggs, whose eggs have not yet reached maturity, 
and only one or two from which ripe eggs can be obtained. Very often only a small 
number of ripe eggs can be obtained when the fish is first squeezed, afterwards unripe 
eggs escaping. This proves that the eggs in the ovary are not matured all at once, 
but in gradual succession. But the process of ripening seems to become more rapid 
towards the end of the spawning period in a given fish than at the beginning, and the 
eggs are evidently extruded immediately after they are ripe ; for although I have 
examined large numbers of female soles which yielded a few dozen ripe ova, and whose 
ovaries al^er the extrusion of these remained distended with unripe ova, I have only 
once found a specimen whose ovaries contained ripe ova only. Tliis specimen was 
captured in a small-sized trawl worked from a Newlyn drift-net boat, on the morning 
of March 23, 1889. I squeezed several thousand ripe ova from it, and the ovaries 
were then completely empty. When uU the ova of one season are shed the ovaries 
are left as flaccid sacs which soon shrink considerably in size. Fish in this condition are 
usually said to be " spent " or " shotten": the latter is the Scottish expression. The 
specimen just referred to was of very large size. It measured 20^ inches in length, 9i in 
breadth. The boat by which it Was taken was trawling at a depth of about 30 fathoms 
on the north-west side of Mount's Bay, off the coast of the Land's End pi-onioutory. 
At the same haul, and in others previously made, shotten females, partially ripe and 
unripe females were taken. The only conclusion to be drawn fi'om these facts is that 
only a few ova are ripened at a time in a given female at the earlier stages of the 
spawning process; while at the later stages though a large number of ova are ripened 
at one time they are very soon shed, and therefore the capture of a female at the par- 
ticular moment when she contains a large number of ripe ova is a rare occurrence. 

As stated above the spent condition of the female is easily recognised, ami when 
only spent females are captured the end of the spawning period for the species is 
determined. I investigated the duration of the period during the two successive 
seasons of 1888 and 1889, and found that it ended some weeks earlier in the latter 
year than in the former, a fact which can only be explained by the warmer weather 



117 



and consequently higher temperature of the sea in the spring of 1889. In the latter 
year, when on board a trawler south of the Wolf Eock which lies to the west of the 
Land's End, on April 11 and 12 I found nearly all the female soles completely 
spent, a few containing nothing but a small number of ripe ova. The surface tempera- 
ture of the sea at that time and place was 48°-5 F. (9°-2 C). In 1888 the fisherman in 
the service of the Plymouth Laboratory obtained ripe soles on April 26 and 27 at a 
distance of 40 miles north of the Land's End where the surface temperature was 46°-0 F. 
(7°-7 C.) and the bottom temperature at 50 fms. was 45°-0 F. (7°-2 C). The temperature 
on April 6, 1888, to the south of the Wolf Eock was 46°-0 F. (7°-7 C). The following 
temperatures of the surface of the sea wiU show the difference of the two seasons : — 



18 8 8. 


18 8 9. 


March 6. 
April 4. 
May 10. 


S. of Wolf Rock .... 
)j >i .... 

M .) .... 


F. 


C. 


March 1. 
April 9. 


S. of Wolf Eock .... 

»1 » .... 


F. 


C. 


45° -8 
45° -5 
50° -1 


7° -6 

7° -5 

10° -0 


48° -0 
48° -5 


8° -8 
9° -2 


March 26. 

„ 29. 

April 9. 

Mav 31. 


S. of Plymouth Breakwater 

» )> >» 
Plymouth Sound .... 
S. of Plymouth Breakwater 


43° 
43° -5 
44° -0 
49° 


6°-l 
G°-3 
6" -6 
9° -4 


April 3. 

Mav 15. 

„" 21. 


S. of Plymouth Brealiwater 


46° -0 
54° -0 
56° -5 


7° -7 
12" -2 
13° -6 



I have not determined so exactly the commencement of the spawning period in the 
two seasons. In 1888 I examined several soles taken nine or ten miles W. by S. 
of the Eddystone, on February 6. Only one yielded a few ripe ova, about a dozen ; 
the rest were all unripe. 

It is thus evident that the spawning period of the sole extends from the middle of 
February to the end of April ; but that the greater number of individuals shed their 
spawn in March, and the eai'ly part of April ; and that in warm seasons the spawning 
is completed by the end of the second week in April ; while in colder seasons some 
individuals are found still spawning up till the end of April, and a few eggs may not 
be shed till the middle of May. 

Little has yet been said about the males. Necessarily the male reproductive 
elements consisting of the fluid milt, which contains the innumerable spermatozoa, 
are discharged at the same period as the ova. But the testes and the milt of the sole 
differ remarkably from those of any other marine fish I have examined. In other 
fishes the testes in the spawning season are much enlarged, and very soft, so that 
when the fish is opened very slight handling tears or ruptures the testes, causing the 
escape of a thick viscous opaque white fluid, the milt. When the ripe male fish i.s 
gently squeezed the milt escapes from the genital aperture in large white drops 
having the appearance of milk, which when allowed to fall in sea water mix with it 
and render it turbid. But when a male sole is opened in the breeding season the testes 



118 

are neither much enlarged nor soft : they present much the same appearance as at any 
other time of the year, though spermatozoa may be seen in a portion examined 
under the microscope. And when the male is squeezed in the region of the testes, no 
milk-white fluid is seen to escape ; some fluid may, and does, escape, but it is small 
in quantity and ihin and transparent, so that it is almost impossible when handling 
soles on board a trawler to distinguish milt thus squeezed out from the sea water, 
urinary fluid, or mucus from the skin, which also drijj from the fish. 



II 



119 



CHAPTER V 

DEVELOPMEXT AND GROWTH. 

The eggs of fishes do not develop unless acted upon by the milt of the male. In all 
species of marine bony fishes, with very few exceptions, the eggs do not come into 
contact with the milt until after they have been discharged from the body ot the 
female; the whole process of development takes place outside the body of the parent in 
the water of the sea. Wlien the egg of a bird is laid it requires only to be kept at a 
certain constant temperature to develop into a chick. When the egg of a snake or lizard 
is laid it develops at the natural temperature of the air without any additional warmth 
derived from the mother's body, and after a certain time a young snake or lizard is 
hatched from it. When the egg, or "purse," of the skate is laid, or taken from the 
body of the mother, it develops into a young skate as it lies at the bottoiii of the sea, 
or in an aquarium tank. In the spiny dog-fish {Acanthias vulgaris), the eggs develop 
within the oviducts of the female, and do not escape tiU they have reached the 
condition of actively moving young dog-fish, in all respects except size resembling 
their parents. But in all these cases the egg has been acted upon by the milt of the 
male while still within the body of the female. When ripe eggs are pressed 
from the ovary of the female sole into clean sea water they do not develop into 
young fishes, but after floating for a few days in the condition previously described as 
that of the unfertilised ovum they die, sink to the bottom, and decompose. This 
proves that the eggs of the sole are not fertilised or acted upon by the male repro- 
ductive elements within the body of the mother, but only after extrusion. 

I have not been able hitherto to observe the natural process of shedding and 
fertilising the eggs of the sole in living specimens in our tanks, and it is of course 
impossible to observe the process in living soles in the sea. It is kno^vn that in 
pelagic fish, like the herring, the fish spawn while collected in crowded shoals, 
males and females being mingled together, and that the females simply shed their eggs, 
and the males their milt into the water near the bottom simultaneously. The water 
into which the eggs pass is thus teeming with spermatozoa, and none of them 
can escape fertilisation. But in the herring the testes are as large as the ovaries, 
and the ([uantity of milt produced by a single fish is very large. In most flat-fishes 



120 

the testes are smaller than the ovaries, but still they are of considerable size, 
and a considerable quantity of milt is produced. When we consider the small size of 
the testes in the sole, and the small quantity of milt produced by a single male, it 
seems difficult to understand how the large number of eggs produced by a single 
female get fertilised at all. It seems to me that the only way to explain the facts is 
to suppose that soles pair together like birds, or at least that the males do not like 
some other fish shed their milt into the water at random, but shed it in the immediate 
neitrhbourhood of a female at the moment when she discharges some ova. Some of 
the wrasses pair and shed their milt in tliis way : I remember watching the process 
once in one of the tanks of the Naples aquarium, but I do not remember to what 
species the fish I saw belonged. 

After I had drawn the inference that some kind of direct fertilisation took place in 
soles, I found my opiiiion supported in a curious way by a statement of Nordmaii in 
his description of the fishes of the Black Sea, published in 1840 (see DemidofTs " Voy. 
Euss. Merid. Zool., Ill, Poissons," Solea nasuta). The statement I refer to is that the 
male and female of the species called by Nordman Solea nasuta, which is, as far as I 
can see, the same as the Solea lascaris of the English coast, during copulation 
adhere together by means of a glutinous liquid, and are sometimes taken in the nets 
in this condition. 

The ripe ova pressed from female soles during the spawning period, when i)lac('d in 
a bottle containing sea water taken from the surface of the sea at the place where the 
fish are caught, float at the surface of this water. That ova so obtained are perfectly 
ripe and uninjured by the artificial method by which they are taken from the fish is 
proved by the fact that when milt is added to the water the eggs are fertilised, and 
when taken on shore and kept in proper conditions will go on developing until they 
hatch into normal young fisli. Tliis is tlie process of artificial fertilisation which will 
be more fully considered in the next section. The observation of artificially fertilised 
ova kept in aquaria shows the rate at which the development proceeds at a given 
fenq:)orature, for it must be noted that the rate of development of all fishes' ova varies 
considerably according to the temperature of the water in which they are contained. 
The ft)llo\ving are the details of my observations on artificially fertilised ova kept in 
aquaria : — 

May If), 1888. — Two or three soles' ova fertilised south of the Wolf Eock at 
4 p.m. Temperature of surface of tlie sea, 50° F. (10° C). 

May 19. — One of the above ova still alive: the blastoderm had completely 
enveloped the yolk, and the dorsal rudiment with Kupher's vesicle was 
completely formed. Temperature in hatching jar, 5;^»'^0 F. (11"''7 C). 

March 23, 1889. — Several thousand soles' ova fertilised off" the Land's End promon- 
tory at 7 a.m. Temperature of the sea water at surface, 48°'2 F. (t)°-0 C). 
Eggs placed in hatching jar at the Laboratory the same evening. 



121 

March 24. — Examined the eggs ; found segmentation completed, the blastoderm 
commencing to spread over the j-olk. Temperature of water in tlie hatching 
jar, 50°-l P. (10"-1 C). 

March 25. — Blastoderm covering three-fourths of the yolk. Temperature the 
same. 

March 26.— The yolk completely enveloped by the blastoderm, stage shown in 
PI. XV, Fig. 4. 

March 27.— Eggs all dead. 

March 29. — Six soles' ova obtained from surface of the sea in stage just after the 
closing of the blastopoi-e, that is, after the envelopment of the yolk by the 
blastoderm. Placed in a small jar with water at 50°-3 P. to 53°-6 P. (10°-2 to 
12° C). 

April 5 and 6. — Three of the above eggs hatched. 

The eggs last mentioned were at about the same staeje when first obtained as the 
previous lot when they died. It may be inferred therefore that at the temperature 
above given, about 50° to 53° P. (10° to 12° C), soles' eggs would hatch ten or 
eleven days after fertilisation. The following experiment is more complete : — 

April 11. — 12.5 a.m. Several hundred ripe eggs obtained from soles trawled 

south of the \Yolf Rock : artificial fertilisation attempted with testes taken from 

the males and crushed in the water. Temperature of surface water of the sea, 

48°-5 P. (9°-2 C). 
April 13. — Eight of the above eggs found to be fertilised and developing; 

temperature of the water in the bottle in which they were carried, 9'5 C. 

These were transferred to a small jar in the Laboratory ; temperature, 10°'0 C. 

Density of the water brought from south of Wolf Eock, 1'0271. Density of 

aquarium water, 1'028. 

April 16. — Two of the eggs killed for investigation; one died. Temperature in 
aquarium, 9°'0 .C, 

April 17. — Temperature in aquarium, 9°"2 0. 

April 18. — Temperature in aquarium, 9°' 7 C. 

April 20. — Two of the eggs hatched out. 

Thus two of these eggs hatched on the tenth day after fertilisation in water at a 
temperature of 48°-0 P. to 50°0 P. (9° to 10° C). Now, as I have shown, the spawning 
period of the sole terminates sooner or later according to the temperature of the sea, 
and scarcely any ova are shed after the temperature lias risen to 50°-0 P. At the 
beginning of the spawning period, in the latter half of Psbruary, the temperature is 

K 



122 

from 43° to 45° F. (6°1 C. to 7°-2 C), and at this temperature the ova would probably 
take between two and three weeks to hatch. 

It is certain that the eggs of the sole do undergo the same development at about 
the same rate in their natural condition as they do in experimental conditions. For 
the characteristics of the sole's ovum having been observed, nanieh', the size, the layer 
of segments in the yolk, and the groups of minute oil globules, it is possible to identify 
ova found in the sea possessing these characteristics as those of the sole. The surface 
waters of the sea ofi" the coasts of Devon and Cornwall contain nearly all the year round 
vast numbers of buoyant fishes' eggs. These can very easily be collected by slowly 
towing through the water from a boat a conical net made of muslin or silk bolting 
cloth. Anion" the ejisrs so collected those of the sole are found in small numbers in 
March and April, sometimes at the end of February or beginning of May, but at no 
other time of the year. 

The development of the sole within the egg is rather slow compared to that of 
some other flat-fishes. The eggs of Pleuronedes Jlesus, the flounder, hatched in my 
hatching jars in six days at a temperature of 50° F. (10°'O C.) ; the eggs of the plaice 
{Pleuronedes ^j/ato5«) hatched in 10 days at the same temperature; those of 
Pleuronedes mici-ocephalus, the merry-sole, hatched in eight days at a temperature of 
about 49°-l F. (9°-5 C). 

I have never found the ova of the common sole very numerous among the pelagic 
ova collected by means of the tow net. The largest number I have obtained at one 
time is six : these were taken a little to the south-west of the Mewstone. 

The density of the water in which soles' ova are found suspended at sea varies 
slightly in difl'erent places. Examples of water from the sea to the south of the Wolf 
Eock I have found to be 1*027 (distilled water being 1*0), while samples from the sea 
ofl" Plymouth, inside the Eddystone, have a density of 1-0267 or r0268. I found in 
my experiments that the sole's ova frequently sank in the aquarium water towards the 
close of their development, that is shortly before they hatched, and that the larvse 
lay on the bottom of the jar after hatching : yet the density of this water was 1'027. 
This shows that the eggs become heavier as development advances, though the 
sinking of the eggs is probably hastened in the hatching apparatus by the accumu- 
lation of particles of sediment upon them. The eggs themselves certainly float in the 
sea until they are hatched, for they are frequently taken in the tow net when just 
ready to hatch. 

I have not been able to keep the larvaj alive more than a day or two after hatching. 
In fact, owing to the difficulties of artificial fertilisation I have never had a sufficient 
number to experiment with. I have been equally unsuccessful in procuring the larvse 
from the sea: it is probable that soon after hatching the larvas sink towards the 
bottom. Some of the stages given in the illustrations to this book of the larva; of 
other species of ffat-lishes show that at first one of the most obvious changes which 
takes place after hatching is the absorption of the yolk. Nourished by the yolk thus 



123 

absorbed the larva developes in all its organs. The pectoral fin grows into a large 
semicircular paddle, the length increases, the black pigment of the eyes (in the 
choroid) is developed, and the jaws acquire their definite structure. When the sole is 
first hatched it has no mouth, and takes no food : the mouth is developed before the 
3-olk is absorbed, but not until the absorption is completed does the young fish begin 
to feed. The newly hatched sole is 3'55 to 3"75 mm. long, between |^th and v^ths of 
an inch. It is perfectly symmetrical, having an eye on each side of its head, and 
swimming vertically in the water, but it swims with its ventral edge uppermost, 
because the yolk is lighter than the back of the fish. 

The next stage in which I have discovered the young sole is immediately after the 
completion of its metamorphosis, that is, after it has ceased to be symmetrical and to 
swim vertically in the water, and has taken to lying flat on the sand, and has both 
eyes on the right side of its head. I had searched everywhere for larval soles at the 
bottom of the sea, after the eggs had disappeared from the surface, and had had a 
special trawl with very small meshes made to capture them with, but could not 
discover any. At last I obtained some through the assistance of Mr. Matthias Dunn, 
of Mevagissey, who has been for years the friend and counsellor of all naturalists 
engaged in the study of British fishes. On April 3, Mr. l)unn sent up to the Plymouth 
Laboratorj' a number of young living flat-fishes. I found on examination that these 
were all Pleuronectes flesus, the flounder. Some of these were very transparent and 
only partially metamorphosed, the left eye being still on the lower side, but near the 
edge of the head ; in others the eye was actually in the edge of the head, looking 
horizontally outwards. Mr. Dunn said nothing about soles, in fact at this time there 
were no young soles in process of metamorphosis. Having failed to obtain young 
soles by trawling, I wrote to Mr. Dunn, and arranged with him to meet him at 
Mevagissey and examine the place where he caught his young flounders. I went to 
Mevagissey on May 15, and found that the young flounders were found in thousands, 
if not millions, in the pools and runlets left at low water during spring tides on the 
bottom of the harbour. The old harbour at Mevagissey (a new additional outer 
harbour was then being built) is completely emptied of water at the ebb during 
springs, and the bottom consists of sandy mud. I went over the harbour with ilr. 
Dunn, and caught numbers of the young flounders with an ordinary cup. The little 
fish are in constant motion, some of them continually rising to the surface of the 
shallow pools in the sand and then sinking again to the bottom. We found a few 
soles along with the innumerable flounders. Many of the flounders were still 
transparent and only partially or scarcely at all metamorphosed, but in all the soles 
the metamorphosis was complete. On this day I only caught three young soles, but 
the following day Mr. Dunn sent to me at Plymouth fifteen more. These young soles 
were from 12 to 15 mm. long: their characters are represented in PL XVI, 3, 
which is 83 times the natural size. They possess nearly all the characters of the 
adult, the chief exception being that the intestine is simpler and shorter, its coils only 



124 

extending back a little behind tlie anterior end of the ventral fin. The eyes are both 
on the right side as in the adult. The skin and body are more transparent than in 
full-grown soles, but the pigment of the upper side exhibits perfectly the arrangement 
of spots which characterises Solea vulgaris. 

On May 17, I examined at low water the shores of Sutton Pool and the mouth of 
the Cattewater in order to find out whether young flounders or soles were to be seen 
in the tidal pools there, as in the harbour at Mevagissey. I could not find a single 
specimen, but the next day some boys brought me two specimens of young flounders 
{PL Jlesus) taken at low tide on the shore of Sutton I'ool. 

Tliese young soles, 12 mm. long, from Mevagissey could not have been more than 
two months and a half to three months old, if the eggs from which they grew were 
shed at the middle of February or the beginning of March, tliat is at the commence- 
ment of the spawning period of the sole ; and it is very probable that they were only two 
months old or even less. As the larvae are not hatched until a fortnight after 
fertilisation, we may conclude that the metamorphosis occurs within about six weeks 
after hatching. 

At the next spring tides, namely, on May 31, Mr. Dunn sent me up some more 
young flat-fishes from Mevagissey harbour: among these was one young sole, the only 
one he could find, it measured | in. (18 mm.) in length. After this he could find no 
more young soles in the tidal pools : they all disappeared, having either left the shore 
for deeper water, or having become strong enough and active enough to swim away 
with the retreating tide and avoid being left between tide marks. During the 
fi)llowing months I perseveringly endeavoured to capture young soles in their later 
stages. I trawled with my specially constructed trawl in Whitsand Bay frequently 
both by night and day, and also in Cawsand Bay and other sandy parts of Plymouth 
Sound, but I never got any young soles. In Whitsand Bay at night I got a large 
numl:)er of young plaice, pouting {Gadus hiscus), and other young fishes, but not a 
single sole. 

Mr. Dunn having told me that he believed there were large numbers of young soles 
in the estuaries of the Fal and Ilelford rivers, I asked my friend Mr. Eupert Vallentin, 
of Falmouth, to make investigations and see if he could find any specimens. Mr. 
Vallentin accordingly made a most careful and complete examination of the two 
estuaries ^^ith the following results. He went to Malpas, a place about two miles 
below Trurt), and there found one man, the innkeeper, who possessed a seine which 
he used for taking flat-fish. On the 27th July Mr. Vallentin had a series of hauls 
made with this seine, the meshes of which were so small as only to admit the tip of 
tile little finoer. After several hauls the total catch of flat fishes was: 
Four Flounders from 8 to 12 inches long, 
Four Soles, 5jj inches, 5| inches, G inches, 7| inches in length. 

The two smallest of the soles were sent to me, and I was able therefore to make 
certain that they were really Solea vulgaris. 



125 

Mr. Vallentiu next on July 29, had a large seine sixty fathoms long and two 
fathoms deep hauled in the Helford Eiver ; two hauls were taken, and a number of red 
mullet and flounders were taken, but only one sole, which was sent to me. It was 
4-j^e- inches in length. 

Now it is obviously impossiljle to believe that young soles which were f inch in 
length on May 31, ct)uld have grown to 5 inches in length by the end of July. Tlie 
growth of flat-fishes is not so rapid as that. The spawning of the jilaice at Plymouth 
takes place in February, and is completed early in March. On June 17, 1889, I 
obtained a large number of young plaice by trawling at night in Whitsand Bay ; these 
measured If to 2-^-g inches (3'4 to 59 cm.) in leogth ; another specmien which I got 
from Sutton Pool on September 28, measured 2-j^ inches (62 cm.). On May 16, 
1889, I obtained a large number of small plaice from the Cattewater, where I saw 
them caught in a small seine : these measured 4| to nearly 7 inches in length. It is 
evident therefore that these last specimens were more than a year old, namely, fifteen 
months, and it is obvious that the soles caught by Mr. Vallentin were sixteen months 
old, reckoning from the end of March as the spawning time. They were soles in the 
second year of their growth. I have in my collection another small sole, measuring 
4| inches (12-5 cm.) which was caught either in Plymouth Sound or on the trawling 
ground off" Plymouth, at the end of February, 1888. Tliis must have been just a year old. 

Why I have failed to obtain soles in the first year of their growth, after the stage 
of those found at Mevagissey in May, I cannot understand. It may be owing to some 
peculiarity of habit, that though I obtained young plaice and other species of flat- 
fishes by trawling in shallow water in Whitsand Bay, I caught no soles. Of course 
soles in the neighbourhood of Plymouth are much less numerous than plaice, flounders, 
dabs, or merry-soles (PL microcephahis), and this doubtless adds to the difiiculty of 
finding them. However, the problem will, I hope, be solved next year. 

It has been shown that the young soles spawned in March have completed their 
metamorphosis by the middle of May, when they are ^ to -^ inch in length (12 to 
15 mm.); that on May 31 they are about f inch long (18 mm.); and that in one 
year they grow to about 5 inches in length. We have now to consider their subsequent 
growth. 

Soles of small size but larger than any of those just mentioned are taken in 
Plymouth Sound in considerable numbers by the small shrimps trawls, which have a 
beam of 12 to 15 feet in length. Such trawls are regularly worked in the Sound for 
shrimps and prawns, and one of them is regularly used for the collecting work of our 
Laboratory. On May 10, 1889, the Laboratory fisherman took with the shrimp 
trawl in the Cattewater, six soles measuring 6| to 7f inches in length (17-1 cm. to 
19-G cm.). Another caught on May 6, measured 9-^ inches (23-3 cm.). I consider 
these soles to be just over two years old. Soles from this size upwards are almost 
always to be caught in the Sound, but the larger are less plentiful. They are never 
very abundant, but usually about half-a-dozen can be caught in a day's work. 



12G 

Adult soles, as sold in the market, vary from about 12 to 16 inelies in length (30 
to 40 cm.). If we take the medium size, 14 inches (or 35 cm.), it is evident that this 
size cannot be reached in one year more by soles which at two years are only 6f to 
9 inches in length. In all probability the length of 1 4 inches is not reached until 
after the fish is four years old, and at three years it is only about 1 1 inches long. 

The difficulty of distinguishing the ages of soles after the first year is due to the 
fact that at a given time a series of sizes may be found from those which are probably 
two years old to those which are three. The explanation of this is, first, that the 
spawning time lasts altogether at least two months, and that the rate of growth 
doubtless varies in different individuals according to the amount of food they have 
been able to obtain. 

The largest sole I have ever seen was one I obtained when trawling off the Land's 
End in March, 1889. It was a ripe female, and measured 20^ inches in length, 9^ 
in breadth (52 cm. by 24 cm.). But still larger specimens have been recorded. 
According to Day a Mr. Grove, of Charing Cross, received one from Torbay in 1882, 
which was 24 inches (61 cm.) long, and weighed 6^ lbs. Yarrell mentions one taken 
to the Totness market in 1826 which was 26 inches (66 cm.) long, 11^ inches 
(29-2 cm.) broad, and weighed 9 lbs. Probably the sole, like most fishes, goes on 
crrowing as long as it lives, and taking the growth as 3 inches a year after the first 
year, when it grows 5 inches, the fish I saw, which was 20^ inches long, must have 
been six years old. 



Part IV. 



ECONOMICAL. 



129 



CHAPTER T. 

ARTIFICIAL PROPAGATION. 

The commonest and most obvious method of attempting to increase the supply of a 
valuable fish is to hatch its eggs. The young when hatched may be disposed of in one 
of two ways. They may be kept in captivity and regularly supplied with food until 
large enough to be valuable, or they may be set free in the natural haunts of the 
species so as to replenish its numbers. The question of the best way to increase the 
supply of soles will be fully discussed subsequenth'. At present I shall describe my 
own experiments on the artificial pi'opagation of the species. 

In the case of a number of species of valuable marine food-fishes there is no great 
difficulty in obtaining large numbers of eggs from the fish, fertilising and hatching 
them. The eggs become ripe at the spawning period, and it is perfectly easy to tell 
whether the eggs of a given species are ripe or not. The number of eggs which ripen 
at one time varies in different species. In some, as the herring, nearly all the eggs 
become ripe simultaneously. When the eggs are ripe they can be squeezed out of the 
ovary by gently stpieezing the abdomen of the fish with the fingers and thumb. They 
run out in a continuous stream, and no blood or membranes escape with them : if the 
eggs are not ripe no eggs escape unless considerable pressure is applied, and when they 
are forced out they are accompanied by blood and by membranes containing blood 
vessels. When the eggs in the ovary all ripen simultaneously, or nearly so, as in the 
herring, the ovaries can be entirely emptied by gentle jDressure. In all fishes that I 
have examined, the number of eggs ripe at the same time increases after the spawning 
has commenced, so that the ovaries after a certain number of eggs have been shed 
contain ripe eggs only and can be entirely emptied. In the cod family the ripening of 
the eggs goes on very gradually, so that only a portion of the eggs in the ovaries of a 
female can be pressed out at one time. The eggs of the sole ripen gradually at first, 
but after spawning has commenced and some of the eggs have been shed the rest all 
ripen simultaneously. The eggs also seem to be shed as soon as they are ripe. These 
are the conclusions I form from my experience, which is that I have usually met with 
soles whose ovaries were either full of unripe eggs and yielded very lew which were 
ripe, or else were quite empty, all tlie eggs having been shed. 

I commenced my experiments on the st)le in 1888. At my first attempt, which was 

s 



130 

on a trawler to llie west of tlie EtUl3'stone on February G, I cot a few, verj- few, 
ripe ova, and could get no milt by squeezing any of the fish. I did not then know that 
the testes were small and the milt small in quantity in ihe sole. Only two or three of 
the ova then obtained were found to be floating in my bottles when I returned to shore, 
and none of these were fertilised. My next attempt was on ^larch and 7, when 
I was on a trawler to the S.E. of the Wolf Eock. Only two or three females out of 
nearly a hundred were then found to yield ripe ova, and as I could squeeze no milt 
from the males, I cut out the testes, cut them into two or three pieces and placed them 
in the bottles with the ova. On my return to Pl3niioutli on March 8, I found only 
about a dozen ova floating, and of these onlj' two or three were fertilised and showing 
the commencement of development. I made another attempt on the same fishing 
ground between April 3 and 7, but on my return found that not a single ovum 
was fertilised. On this occasion I got a considerable number of rij)e eggs altogether, 
but onlj' a few from each fish. From May 1.5 to 18, when I was in a trawler on 
the same ground, we had verj' bad weather : nearly all the soles were spent, but some 
ripe ova were obtained from one specimen, and three or four of these were found to 
be fertilised by the pieces of testis. 

It seemed therefore from these experiments made in 1888 that the artificial fertilisa- 
tion of soles' ova was a matter of the greatest difiiculty. T had succeeded in ascertaining 
the characters of healthy fertilised ova from the few I had been able to procure, and 
was therefore able to identify the sole's ovum when it occurred in the produce of the 
tow-net, and I had also observed and made drawings of some stages of the development, 
but this, though valuable knowledge, brought me very little nearer to the practical 
object of my experiments. 

In the season of 1889 I continued the experiments. I had found that soles were 
scarce on the Plymouth trawling ground, which extends from the Dodman Point in 
Cornwall, to the neighbourhood of Bolt Head in Devon, both inside and outside the 
Eddystone. On this ground very often no soles at all are found in a haul of the traAvl, 
and when there are some very often all are immature, or when a ripe female is taken 
there are no males. On February 12, 1889, I was on a trawler which towed her trawl 
from ofl' Eooe to a ])oint south of the Plymouth Breakwater lighthouse : four soles 
were taken in this haul of which only one was adult, and that not ripe. On March 14, 
I went out again, and this time the trawl was worked about 10 miles south of the 
I'ddystone. Two hauls were made : in the first there was one sole, in the second none, 
although the first haul was made in the night. After this I heard that some of the 
Xewl3Ti mackerel boats were working small trawls in Mount's Baj" in order to earn 
something while waiting for the commencement of the mackerel season. I therefore 
went down to Penzance by rail, taking with me a number of collecting bottles to bring 
back soles' ova. I went out in one of the boats on March 22. On this occasion I 
examined tlie testes very carefully. I tried a large number of males, and could not 
squeeze from an}- of them the thick milk-white milt which is so characteristic of the 



131 

ripe males of other fishes I have exaiuiued. Licjuid came from them of course, and in 
some cases it had a slightlj^ milky appearance, but it was never possible to distinguish 
the milt derived from the testes from the urine coming from the urinary bladder. It 
was therefore useless to squeeze a male sole over a bottle containing ova in order to 
fertilise them, for it was impossible to know whether any milt entered tlie bottle or 
not. I dissected out the testes themselves from several specimens, and cut them iu 
half and crushed them between my fingers, and found that all the liquid that came 
from them was thin and almost clear, only very slightly turbid. It is evident, therefore, 
seeing that these testes came from ripe males, that the sole does not produce any milk- 
white thick secretion such as constitutes the milt of other fishes. The milt of the sole 
is not only very limited in quantity, but is a thin liquid only slightly turbid, which is 
difficult to distinguish when the male is squeezed. A considerable number of soles 
were taken on this excursion. Some of the females were spent, some unripe, some 
yielded only about a dozen ripe ova. But one female, the largest specimen I ever saw 
{see page 126) yielded several thousand ripe ova. The ovaries of this specimen con- 
tained ripe ova only : she was at the last stage of spawning, and probably these ripe 
eggs were nearly half the entire number produced that season, the rest having already 
been shed. Having fully investigated the males I concluded that the only method 
likely to ensure fertilisation was to extract testes from the male soles, and crush these 
up into a pulp between my fingers in the water into which the ova were to be allowed 
to fall. In this way the whole of the milt contained in the male organs was sure to be 
set free in the water containing the ova. I found this method perfectly successful. 

At the Laboratory there was now a constant circulation of sea-water, and apparatus 
for hatching floating ova which had been found to work admirably. The year before 
the Aquarium was unfinished and there was no constant supply of sea-water. I landed 
at Penzance with fertilised soles' eggs on the morning of March 23. The eggs were 
contained in short wide glass jars such as are used foi- conveying sweets : over the 
mouth of each was tied silk bolting cloth to prevent the eggs escaping, and this, to 
some extent, prevented the water splashing over. I placed the bottles, held in a 
divided basket, in the break-van of a train, and took them to Plj'mouth, where I arrived 
the same evening. The eggs were at once placed in the hatching jars ; they seemed 
quite health}-, and microscopic examination showed that they were all fertilised. 

The apparatus and method I adopted last spring for hatching floating eggs were as 
follows : — The apparatus is a modification of that recommended by II. C. Chester, of the 
United States Fish Commission.""' The arrangement of Chester's apparatus is represented 
in Fig. £" (p. 132) : it consists of a tall glass jar, j, which has an open narrow neck 
above and is widely open below. This is placed in a tank having a constant supply of 
sea-water, the overflow of which takes place through a siphon tube, s, having a diameter 
greater than that of the inflow. The water in the jar is of course always at the same 

Vide '• Devel. Osseuus l-"islics," by J. A. Racier, Rep. U. S. Fisli Coniuiissiou for 1885, p. 400. 



13-2 



level as the water in the tank. When the siphon of the outflow tube is empty the 
water in the tank and jar rises until the level of its surface reaches the bend of the 
siphon. Then the siphon fills and commences to act and the level of the water sinks 
gradually until it falls below the short leg of the siphon, when the latter empties and the 
outflow stops. The wide opening at the bottom of the jar is covered with a single 
thickness of coarse cheese cloth to prevent the escape of the eggs which are introduced 
into the jars through the narrow opening of the neck above. The rise and fall of the 
water is only five inches vertically. Eyder says that cod eggs were hatched in this way 
with a loss of only five per cent. I tried this apparatus with a large number of eggs 
of the flounder and plaice {Pleuronectes fiesiis and P. platessa). 





Fig. £. Fig. F. 

Fig. E. DiagraTD of a transverse section of an apparatus for hatching buoyant fish eggs, arranged 

according to the method devised by Captain Chester, of the United States Fish Commission. 
Fig. F exhibits the modification of the apparatus adopted in the Laboratory of the Marine Biological 
Association. 
j, The glass hutching jar, resting on two bricks in a small tank containing si?a-\vater ; o, the overflow 
tube; s, si])lion in the overflow tube; /, an iudiarubber tube conducting the inflowing water 
into the interior of the hatching jar. The dots represent the eggs. 

On February 12 I placed a large number of ova of the flounder, artificially 
fertilised the same day, in two glass jars of the form described. The jars were 8 inches 
wide and 17 inches high. The bottom of each jar was covered with silk bolting cloth. 
Each jar was supported on two bricks resting on the bottom of a shallow aquarium tank 
made of slate and glass. The water escaped from the tank by a stand pipe into which 
I fitted a glass siphon so that the level of the water in the tank oscillated between limits 
about 4 inches apart. The water in.side the jar was of course perfectly stiU : its 
gradual rising and sinking caused no disturbance in it, in fact I found that the upper 
part of the water in the jar was scarcely changed or affected by the rise and fall. 
This will readily be understood. The total height of water in the jar was about 10 
inches : .at the top of this floated the eggs which formed a layer about | inch thick. 
As the level of the water in the tank sank, the water at the bottom of the jar escaj^ed 
through the bolting cloth. \\'hen the tank was at its lowest level the height of the 
water within the jar was still (> iiichos. When the water rose again all this water 
was bodily lifted up with the Liver of eggs at its surface, while 4 inches of new water 



133 

entered the bottom of the jar. Thus the G inches of water simply rose and fell 
gradually without being renewed or circulated : the only change effected in it was that 
which took place at the bottom layers by contact with the new water which entered 
the jar every time the level of the water rose. The upper layer of water containing 
the ova was practically stagnant. The fall and rise of the water occupied each three 
quarters of an hour. 

On February 16 I found that about half the ova in each jar were dead, lying on the 
bolting cloth at the bottom and contaminating all the water that entered the jar. I 
therefore removed these dead ova by means of a siphon, and changed the arrangement 
in one jar. I left the jars in the same position, but removed the siphon from the 
overflow pipe of one tank and introduced into the jar (Fig. F) an indiarubber 
tube, t, leading from a jet supplying clean sea-water. I regulated the force of the water 
discharged by the indiarubber tube. The tube reached just below the lowest level to 
which the water in the jar sank, and the force of the water escaping from it kept the 
ova in constant but very gentle motion. Thus clean water was constantly entering the 
jar and escaping through the bolting cloth at the bottom, and the eggs were separate 
in the water, not in contact with one another in a dense layer. 

On Februarj' 17, I found that all the ova in the unaltered jar, except a dozen or 
two, were dead, while in the jar provided with the new arrangement, only a dozen 
or two out of several thousand had died. But I found that the new arrangement was 
not perfect. The water when its surface fell in the jar left a number of ova adhering 
to the sides of the jar, which were thus for a considerable time out of water. These 
eggs so stranded died. I therefore placed the jar in another tank in which there was 
no siphon in the overflow pipe, so that the water in the tank and jar was at a constant 
level. I made the indiarubber tube delivering inside the jar longer so that the 
water escaping at its end threw it into a regular gentle rhythmical motion which 
served to keep the ova uniformly distributed throughout the water in the jar. I found 
this method answered perfectly. The water in the jar was constantly renewed, and, 
a very important point, no sediment settled on the ova. In fact, the eggs thus treated 
were as clean and transparent as eggs taken by the tow-net from the sea, a result I 
never before obtained with e<i<?s artificially treated. 

On February 18, I found all the ova in the new apparatus had hatched ; in the 
jar left with the original arrangement a few eggs were still alive and some of these 
were hatched, but not all. It seems therefore that the motion of the eggs facilitates 
hatching, as it enables the larva to get rid of its egg shell more easily than it can in 
still water. The number of larva; hatched in the vinaltered jar was quite insignificant, 
not more than a dozen altogether, while in the altered arrangement I had between 
one and two thousand healthy l;irva\ The two jars originally contained about the 
same number of eggs. In a tliird jui- I had placed, on February 12, a large 
number of fertilised ova of the plaice. This jar was arranged on the American plan, 
and was left in this condition without change. On February 10, only about twentv 



1.S4 

of these eggs remained; the rest had all died, notwithstanding that I took care to 
remove all dead eggs every day. 

The arrangement which I adopted and found perfectly satisfactory is shown in the 
dia"ram, Fig. F. It may of course be carried out on any scale, and does not require 
a great deal of space. It is better to increase the capacity of the apparatus by 
increasing the number of the jars ratlier than by increasing the size. Jars larger than 
those I have described become unwieldy. 

I found the method suited the hatched flounder larvae extremely well : they lived 
in the jars in perfect health until the yolk was entirely absorbed. I did not succeed 
in feeding them after that period. It would probably be necessary when the yolk 
was absorbed to turn then out into a larger tank, as feeding in a confined space 
contaminates the water. A few of tlie plaice eggs hatched on February 22, and 
one or two of them lived till the yolk was absorbed in the apparatus arranged on thu 
American method ; but this was the total result out of several thousand ova. 

To return to the eggs of the sole which I obtained in Mount's Bay on March 23. 
I placed tliem in two hatching jars arranged in the way I have described. There 
were several thousand of the eggs, but I did not count them. As I have said, they 
were all fertilised and had commenced to develop when placed in the hatching jars. 
On March 21, when I examined them, I found to my surprise that nearly half in 
each jar were dead. The blastoderm in the dead ones was formed, but some abnormal 
appearances were seen round its edge. I removed the dead eggs, and hoped the 
mortality was over and that the rest would live. But the next day I found again 
half of those left had died. In the living ones the germinal membrane had enveloped 
more than half the yolk : nuiny of them seemed unhealthy. On March 26, only about 
six eggs in each jar were left alive, and these were dying, although in them the 
embryo was already formed. As I had succeeded in keeping eggs of the sole, 
artificially fertilised, ahve for a considerable time with only the roughest apparatus, 
and as I afterwards hatched eggs taken by the tow-net from the sea, the cause of 
death in the above experiment clearly could not be attributed to the water of the 
a(juarium or any of the conditions under which the eggs were kept after they were 
brought to the Laboratory. I could only attribute it to the railway journey which 
had shaken and jolted the eggs and so injured them mechanically. It might be 
su^o-ested that there was too great a dillerence of temperature between the water in 
which the eggs were carried from Penzance and the water of the hatching jars, but 
other experiments showed that eggs taken from the sea lived well in the sea water of 
the Laboratory, and the weather during the railway journey was neither hot 
enouo-h to heat the water in the jars containing the eggs nor cold enough to cool it 
to any extent. 

Believing it useless to carry fertili-sed eggs by rail, I went out on April the 8th, on 
board a trawler which was going to fish on the Mount's Bay ground. On April 11, 
12.5 a.m., the trawl was hauled with seventeen soles in it. Of these I examined 



.).) 



eleven, the rest were not found till afterwards when the decks were cleared up. (Jf 
these eleven, three were temales almost spent but still containing some ripe ova ; one 
was a female still unripe, four were spent females, and three were males. I got 300 
or 400 eggs altogether which I tried to fertilise as before by crushing testes in the 
water. At 4.80 p.m. the same day from six soles taken I got about a dozen more ova. 
On April 12, at 8 a.m., after a good night's haul, fifty-seven soles were brought on 
deck. Of these fifteen were small, under nine inches in length, and not sexually 
mature ; eighteen were males ; nineteen large females entirely spent ; five large females, 
which yielded a few ripe ova. 

I may conveniently refer to the eggs obtained from the different hauls of this cruise 
as lot 1, lot 2, and lot 3. On April 12, while still at sea, I observed that a large 
proportion of the eggs of lot 1, fertilised the previous day, had died and sunk. These 
were probablj' not fertilised, but I do not know why the fertilisation had failed ; it 
may have been because the males were either immature or spent. I found when I 
returned to the Laboratory, on April 13, that only eight eggs in lot 1 were alive and 
developing ; in lot 2 some were floating but none fertilised ; in lot 3 two or three ova 
were alive and developing. 

On April 15, there were altogether nine eggs left alive: of these I preserved two 
for microscopic examination and left the other seven in a small glass jar provided 
with a circulation, not in one of the hatching jars above described, but an ordinaiy 
jar, the only difference in the arrangement being that the overflow of the water took 
place through a protected siphon, the jar standing in the air, not in the water of a 
tank. On April 16, I again went to sea, and returned on April 20, when I found 
of the seven eggs I left in the Laboratory two were hatched, two alive but unhatched, 
and the rest dead. The circulation had almost stopped, the supply tube having got 
choked. On April 21 the two larvte were dead, and one of the eggs: the last egg 
hatched on April 22, but died the same day. 

The above results prove that it is possible to artificially fertilise the eggs of the 
sole and to hatch the eggs so fertilised in a hatching jar provided with a circulation. 
The}' prove also that the cause of the death of the large number of eggs brought from 
Penzance was not in any of the conditions to which they were exposed in the 
Laboratory. The reason that I did not place the seven eggs just mentioned in a large 
hatching jar was that it is difficult to find such a small number in such a jai-, or 
extract them for closer examination. 

PosTSCHiPT (May 3, 1890). While these pages have been passing through the 
press the spawning period of the sole has again arrived, and I have renewed ray 
endeavours to perfect a method of artificial propagation. Li consequence of 
previous experience my success has been greater than in former seasons. During 
a week I spent on a Lowestoft trawler in the Bristol Channel from April 9 to 
April 16, I obtained a large numl)er — hundreds of thousands — of ripe soles' eggs. 



I tried to fertilise these in the usual iiiaiiiier by extracting the male organs and 
crushing them in the water containinpr the ejrgs. On mv return. I found less than 
half the eggs taken were floating, but only about half of these last proved to be 
fertilised. However, those which were fertilised were hatched in the hatching jars 
without ditricully, and I obtained thousands of larvae. Some of the eggs were lost 
before hatching because they ceased to float, and many larvse were lost for a similar 
reason, as they began to sink two or three daj's after hatching. However, a large 
number of the larvas were successfully kept alive until the mouth had developed, 
the yolk was almost entirely absorbed, and feeding had commenced. Then they 
all died. Thus when the eo"s are once fertilised thev can be hatched without 
difficulty. 



137 



CHAPTER II. 



THE SOLE FISHEEY. 



We have next to consider tlie present condition of the sole fishery and to ascertain 
whether the supply of soles in British waters has decreased in recent times. The 
materials available for this enquiry are extremely scanty. Fishery statistics have been 
systematically recorded for manj' years past in Scotland, but as there are no soles, 
except as occasional rarities, in Scottish waters, these statistics are of no use for our 
present purpose. The statistics of Irish fisheries on the otlier hand have only been 
collected at all comprehensively since 1887, and the quantity of soles and other fish 
landed at a certain number of Irish ports is recorded for only two years up to the 
present time, namely, 1888 and 1889. For England and Wales analytical statistics 
have been published in the " Statistical Tables and Memorandum relating to the Sea 
Fisheries, &c." compiled by the Fisheries Sub-department of the Board of Trade, since 
the year 1886. The figures in these tables of the total quantities of soles and otlier 
prime fish landed on the English and Welsh coasts in successive j^ears are given in the 
following table :— 





Soles. 


Turbot. 


Prime Fish not separated. 


Quantity. \ Value. 
Cwts. ! £ 


Average 

price 
per cwt. 


Quantity. 

Cwts. 


Value. ! -^"^g" 
£ 1 price 

per cwt. 


Quantity. 
Cwts. 


Value. 
£ 


Average 

price 
per cwt. 


1 . & s. d. 

1886 . . 98,078 ; 427,452 4 7 2 

1887 . . 85,316 | 389,414 4 U 3 J 

1888 . . 72,522 379,382 5 4 74 

1889 . .; 74,143 431,269 . 5 16 4 


59,850 
63,166 
55,041 
53,576 


£ «. d. 
182,665 3 1 Oi , 

184,662 2 18 5J 

171,967 3 2 5J 

180,841 13 7 6 


370,014 

115,850 

113,415 

35,982 


£ s. d. 
369,089 19 Hi 

368,674 3 3 7i* 

316,966 2 15 lOJ 

126,924 3 10 6i 



V 


m . , « T, • T-.- i II Totals of all Fish except 
Totals of Prime Fish. |1 Shell-fish. 


Quantity. 
Cwts. 


Value. 
£ 


^'■•^.'"S^ Quantity. 

P"<-\ Cwts. 
per cwt. 


Value. A^^™g« 
„ pnce 

per. cwt. 


1886 .... 527,942 

1887 .... 264,332 

1888 .... 240,978 

1889 ... 163,701 

1 


979,206 
942,750 
868,315 
739,034 


£ «. d. 

1 17 1 6,412,433 

3 11 4 6,029,481 

3 12 Of , 6,348,072 

4 10 3 6,464,564 


£ .!. d. 
3,688,079 U 6 

3,778,953 12 6i 

3,948,013 12 5i 

3,862,389 11 US 



138 

All the above figures, according to the explanation given by the officials who 
publiyh the statistics, refer to the fish as landed ; the prices are the " wholesale values 
at the places of landing," by which I believe is meant the prices actually paid to the 
auctioneers who sell the fish for the fishermen and smackowners. The classification 
is made according to the way in which the fish are packed when brought ashore. 
The best and the largest quantity of the soles and turbots are placed in boxes by 
themselves not mixed with any other fish, while if there are not suflicient soles or 
turbots in a catcli to make it worth while to pack them separately they are put 
together with other kinds of " best " or " prime " fish. Therefore the figures under 
tlie heading " soles " do not rei^resent the total quantity of soles landed. There are tons 
of soles and turbot included under the heading of " prime fish not separated." Now, 
if we look at the figures referring to soles only, we find that in the three years 1886, 
1887, 1888, there was an annual decrease of 13,000 cwt., a very startling result. But 
in 1889 there was an increase of nearly 2,000 over 1888. 15ut this latter increase 
is much more than balanced by the enormous decrease in the quantity of miscellaneous 
prime fi.sh in 1889, a decrease of 77,433 cwt. In no year was the decrease in 
the quantity of separated soles balanced by an increase in the quantity of mis- 
cellaneous prime fish ; on the contrary, there was a steady decrease in the latter 
in 1887, 1888, and 1889. The figure of this item in 1886 must be kept apart, for 
in five months of that year haddock were included under it at Billingsgate when 
packed with prime fish, while since then haddock have been estimated separately. 
This alteration also affects the totals of prime fish; but neglecting 1886 there was a 
great annual decrease in the total quantity of prime fish landed. There is no doubt 
therefore on the whole that since statistics have been kept, since the year 1886, there 
has been a steady decrease in the (jnantity of soles landed on the coast of England 
and Wales. I think it is very probable that the slight increase in the quantity of soles 
landed separately in 1889 is due to the fact that in the eai'lier half of this year a large 
number of North Sea trawling smacks left their own grounds and went to work off the 
north coast of Cornwall, on a trawling ground which had previously been almost 
entirely neglected, and on which soles were found in great abundance. This ground 
was first tried bj' some Brixliam trawlers in 1887. 

Another .sure indication of the increasing scarcity of soles is the steady rise in price. 
Tlie price of soles sold separately has risen 45. to 13s. per cwt. every year. Tlie 
price of turbot has not increased so steadily, though there is indication of increasing 
scarcity of this fish also. The price of mixed prime fi.sh is somewhat irregular : that 
of the year 188() is of no value to our iiuiuiiy for the reason Ijefoie nu-ntioned, and 
the prices in other years may and probably do vary with the jiroportion of soles in (lie 
boxes. The average price of prime fish taken altogether has increased steadily. In 
1889 it was 18s. 3c/. per cwt. greater than in 1888. The Board of Trade tables give 
the average price of soles per lb. for each year, and it is interesting to compare the.se 
with the prices for the ten years 1856 to 1865. In the report of tlie Sea Fisheries 



139 

Commission of 1S6G 1 find a table giving the price of various kinds of fisli during tliose 
years both in tlie Manchester Fish Market and that of Newcastle-ou-Tvne. The figures 
are as follows : — 

Manchester. f 1856. 1857. 1858. 1859. 1860. 1861. 

I 3d. to -id. 6d. to 8d. 5d. to 8d. Gd. to lOd. M. to (id. (id. to 8d. 
Soles per Hi. .-\ 

I 1862. 1863. 1865. 

(. 6(/. to 8d. 8d. to lOJ. Gd. to 8d. 

Newcastle. f 1856. 1857. 1858. 1859. 1860. 1861. 

9rf. to 1/3. 1/- to 1/G. 1/- to 1/6. 1/3 to 1/9. 1/3 to 1/9. 1/3 to 1/&. 



Soles per pair 



1862. 1863. 1864. 1865. 

1/6 to 2/.. 1/6 to 2/-. 1/9 to 2/-. 1/9 to 2/-. 



Thus the price in both places was about doubled in the ten years. The average 
prices of soles per lb. in the past four years according to the Board of Trade returns 
are : — ■ 

1886. 1887. 1888. 1889. 

9-Ud. 9-78d. ll-21tZ. l-2-iiJd. 

To compare these with the Manchester prices given above it must be remembered 
that the latter prices are retail, or very nearly so : that is, they are the prices of the 
fish after they had been carried from the landing place to Manchester, and therefore 
include the cost of carriage and the profits of the merchants and salesmen. Thus the 
rise in the price of soles since 1856 is at least from Sd. to Is. per lb., or fouifold : and 
this is not due to any decrease in the value of money, for almost everything else has 
become cheaper. 

It may be urged that the total quantity of all fish landed has not decreased but 
only slightly fluctuated. But this is no compensation for the scarcity and dearness of 
soles. It may be partly due to the greater value of second rate fish caused by the 
diminution in the supply of prime fish, and it may be partly due to the fact that manj^ 
kinds of fish such as herrings, mackerel, and pilchard vary considerably in abundance 
in difierent years from causes which are apparently not connected with fishing 
operations. But soles are stationary fish : they do not move in shoals, nor as far as we 
know move about at all to any great distance, and the only cause to which we can 
attribute the decrease in the supply is constant fishing. The decrease is certainly not 
due to any decrease in the numbers of trawlers, for the trawling fleets grow larger 
almost every year. 

The statistics I have discussed are as far as I can discover all that are available. As 

a nation we ought to be thoroughly ashamed that no statistics worth the name were 

kept either in England or Ireland before the year 1886. Before that time there were 

periodical agitations about some particular kind of fishing which was said by those not 

engaged in it to be injuring the fisheries. These agitations usuallj' arose out of jealousies 

between diflTerent classes of fishermen, and were founded chiefly on prejudice and 

T 2 



HO 

ignorance. The Government of the day appointed Royal Commissions to inquire into 
the questions in dispute. These Commissions proceeded to investigate the matter not 
by considering the facts, for tliere were usually none establislied either of a statistical 
or biological character, but by taking down carefully and printing the statements of 
the disputing lishernien themselves and weighing the assertions of one set against those 
of the other. Of course the Ctmuiissions collected together those facts bearing on the 
matter which were known, and their reports contain a certain amount of grain 
amongst a great deal of cliafT. They also constantly reported that the only satisfactory 
method of investigating problems concerning the fisheries was to study the natural 
history of the fishes and to record fishery statistics. Probably the various Commissions 
cost quite as much as a proper fisheries department, including a scientific as well as a 
statistical staflT, would have cost, but it was the traditional British method to appoint 
Commissions. The public authorities have now commenced to collect and record 
statistics, but they are yet far from the organisation of a satisfactory and convenient 
system. In order to find information about the English sea-fisheries now we have to 
search three distinct publications; the statistics of fish landed are given in the 
" Statistical Tables and Memorandum," the number of boata and men are to be found in 
the Annual Statement of Navigation and Shipping, the preparation of which is entirely 
out of the control of the Fisheries Sub-department, and finally a certain amount of 
miscellaneous information is given in the Annual Reports of the Inspector of Sea 
Fisheries. 

But apart from this inconvenience a great deal of improvement might be effected in 
the system of recording the statistics. The difficulty of finding the total quantity of 
soles landed has been sufliciently obvious from the above discussion. It might at first 
be supposed that all the soles landed were included under the heading " soles," but we 
find on careful examination that some soles are also included in the item of " prime 
fish not separately distinguished." Of course this inconvenience is due to the customs 
of the trade : sometimes soles are sold in trunks unmixed with other fish, while boxes 
of mixed fish, including soles and small turbot, are also sold entire. But at least some 
effort might be made to ascertain and inform the public what proportion the soles sold 
separately bear to the total amount, whether the proportion is approximately constant 
or not. If it has been found possible to separate the haddocks wliicli are sent to 
Billingsgate packed with prime fish, it ought to be possible to separate the soles. 
Another peculiarity in the tables which must shock the mind of anyone engaged in the 
fish trade on the east coast or in London, is that beside the item soles in the figures for 
England and Wales is placed an item in the figures for Scotland which a foot-note 
explains to refer to lemon-soles. Now lemon-soles are no more soles than plaice are, 
and their value is scarcely greater than that of plaice. Besides, quantities of lemon-soles 
are sold in the London market and other English markets, but we are not told where 
they are placed in the English statistics. We do not even know whether they are classed 
as " prime fish not separately distinguished " or not. However, it is very satisfactory 



141 

that complete statistics are now aunually recorded, and it ought to be possible in future 
to find at once whether the supply of a given fish has decreased or increased : the 
importance of this possibility in relation to the trial of any measures, legislative or 
otherwise, intended to maintain or increase the abundance of particular kinds of ILsh, 
cannot be over estimated. 



142 



CHAPTER III. 



PRACTICAL MEASURES. 



The question we have here to consider is : Can soles be made more plentiful by measures 
which are not only possible but practicable, that is, which are sufficiently easy to be 
carried out, when they are understood and have become familiar, without a degree 
of exertion and expense too great in comparison with the results gained? In 
examining into this problem we must distinguish the (wo ways in which human action 
can be applied to a valuable wild animal. One way is to keep the animal under entire 
control by taking it into captivity : this may be called domesticating the animal, the 
word domestication being used with a wide signification, and not necessarily implying 
the taming of the animal. The other way is to leave the animal in perfect freedom, and 
to increase its numbers Ijy protecting it and promoting its reproduction. With regard 
to the sole we will consider the latter metliod first. 

At present our knowledge is much too scanty to allow us at once to reach definite 
conclusions and calculate with certainty the efiects of measures which suggest them- 
selves. We do not know exactly what proportion of soles are usually destroyed in 
nature at different stages of their existence: the proportion which reach adult age 
from a given number of eggs must, we know, be very small. 

We know that the " prosperity," if I may use the word, of a species depends on a 
chain of extremely delicate relations between it and the other species of the fauna and 
flora of its habitat : and we have reason to infer tliat in some cases these relations and 
the species themselves are affected to an enormous extent by i)hysical, i.e., meteoro- 
kxrical conditions over which man has no control. In order to know how man's action 
can increase or maintain the abundance of a species we require to know how his 
action in the past has decreased its numbers. Professor Huxley, in the case of the 
herrinw, for instance, has argued that enormous as is the number of herrings captured 
annually on the coasts of Britain, the evidence leads to the conclusion that the 
number destroyed by man is quite insignificant in comparison with the numbers 
destroyed by the natural enemies of the herring — by the cod and sea-birds and other 
animals which prey upon it. 7\.nd this conchision seems to be supported by a 
comparison of the abundance of herrings in different years. The number of herring 
fishermen, the effifiency of their boats and nets, and the extent of their operations has 



In llie 


year 


1870 


»j 




1874 


5» 




1871) 


}> 




1880 


57 




1881 


!9 




1884 
1888 



143 

increased steadily and largely during the past twenty years. IJut although herrings 
have been somewhat scarcer in some years than others, there is absolutely no evidence 
that the supply has gradually decreased. On the contrary, the following figures will 
show that the supply has on the whole increased as the number, efficiency, and size 
of boats and nets increased, but has not increased continuously in proportion to the 
increase in the apparatus of capture, nor decreased after a certain maximum in 
consequence of the great number annually captured. In fact as far as we can see at 
present the abundance of herrings in different years fluctuates in consequence of 
conditions not only beyond human control, but at present unknown. The number ol 
barrels of herrings cured in Scotland was : — 

833,160 

1,000,5G1 

841,796 

1,473,600 

1,111,155 

1,697,952 

.. 1,118,872 

But, on the other hand, we know that human rapacity and recklessness have entirely 
or nearly exterminated certain species of animals which were at one time very 
abundant in certain regions. The Dodo and the Ehytina were exterminated by man, 
and the Greenland whale and the American bison seem to be rapidh^ approaching the 
same end. The Dodo was confmed to the island of Mauritius, and seems to have 
been more persecuted by the domestic animals introduced by the Dutch discoverers of 
the island than by the Dutch themselves : it could only have been saved by being 
domesticated, and apparently it was not sufficiently valuable to be worth keeping. 
The Rhytina was a kind of Manatee which lived on Behring's Island and Copper 
Island in the Xorth Pacific, and was extremely numerous on the former in 1741, when 
the island was first discovered. It was exterminated in less than fifty yeai's by Russian 
hunters and traders who lived upon its flesh. The Ehytina was of enormous size, and 
quite harmless, and its extinction was doubtless largely due to these circumstances, 
which made its slaughter easy, and to its slow rate of multiplication. 

The history of the northern fur seal of the Bebring Sea is less mournful, and at the 
same time most interesting and instructive. This species, Callorhinus ursimis, breeds 
only on two islands of the Bribylov group off the coast of Alaska, on the ■Connnander 
Islands in Behring Sea, and one other in the same region. The seals arrive at these islands 
late in spring, and remain on shore until the beginning of November. The females bring 
forth their pups soon after landing, and before the mothers leave the islands these pups 
are weaned, and able to tmvel with them. During the winter months the seals seem to 
disperse and live in the sea, but I have found no account of their mode of life during this 
period. In 1870 the Alaska Commercial Company of San Francisco received a lease 



144 

of the Pribylov Islands from the United Slates Government at a rent of §55,000 or 
£11,000 a year, and afterwards rented the other seal islands from the Eussian 
Government. This company since that time has slau^ditered 100,000 seals annually 
on the Pribylov Islands alone, for the sake of their skins, and yet has not diminished 
in the least the abundance of the animals, but rather increased it. Yet it is practically 
certain that if the seal islands had been open to hunters of all nations, considering 
the great value of the skins, the numbers of the species would by this time have 
been seriously diminished, and probably the species would ultimately have been exter- 
minated. Wliat is the reason of the different results obtained by the Company? It 
is tlie story of the goose with the golden eggs. The old male seals are polygamous 
and very pugnacious, and do not allow the young males to possess any wives at all. 
The young bachelors live in a herd by themselves, and only these are killed ; no 
females are destroyed. The check on the number of males is an advantage to the 
species, for when there are too many, the amount of fighting that goes on in the 
" rookeries " destroys a number of cubs. 

In the case of this fur seal a whole species has been practically made private 
property without being in any sense of the word domesticated. It is evidently 
impossible for a company to acquire exclusive possession of the whole of any species 
of marine fish. But our marine fisheries are the property of the nation, and the 
fishermen can be controlled by legislation, if measures can be found which have such 
a relation to the conditions of life and reproduction of the various species as to result 
in benefits both to the fishermen and the whole nation. 

Legal measures have fri^m time to time been taken to prevent the reduction of the 
numbers of valuable marine animals by prohibiting the capture of the young individuals 
below a certain size. Such measures doubtless have a good effect when carried out, 
for, in the first place, small individuals have generally a very small value, while the same 
individuals when full grown are worth many times as much ; and, in the second place, 
if the young individuals are destroyed there will be no parents to succeed those from 
which they were derived. But these measures, however effectively carried out, will not 
prevent the scarcity of a species if the adults are constantly destroyed in such 
numbers tliat there are not enough left to produce sufficient eggs to give rise to rhe 
next generation. The latter has been the case with species of fish which ascend rivers 
and estuaries in order to breed. A measure applied to prevent the too great 
destruction of adults in this case is that of prohibiting the capture of any individuals 
whether young or adult during the breeding period, the institution of " close seasons." 
Now if the regulations concerning close seasons were carried out in regard to the 
salmon in such a way that no adult salmon in a river in a given winter were killed 
until after it had spawned, and all were killed after spawning, and at the same 
time no immature fish were killed, it is clear that the result would be that each 
fish that arrived at maturity would certainly breed once, and only once. And 
there seems no reason why this should not be sufficient to maintain the abundance 



145 

of the species ; for the number of eggs produced by a female sahnon at one spawning 
season is very large. But as a matter of fact the regulations are not enforced 
in this way : the salmon ascend rivers throughout the summer, and do not spawn 
till autumn, and the fish that have recently spawned are of no value. Those that 
are sought are those that have just entered the river. The annual close season 
is limited to the actual spawning period. In consequence it is only those adults 
which escape the net, the hook, and the trap which survive to deposit their eggs and 
milt. However, even thus the close season has a good effect, for it ensures that the 
adults who do escape shall shed their reproductive products in peace and security, and 
the eggs are therefore all fertilised and placed in conditions proper for development, 
while if the fish were disturbed, a greater number would be destroyed, and the eggs 
of those that were left would not be so properly deposited. 

But another method which has been applied to anadromous fish is tliat of artificial 
propagation. This has been successful chiefly in the case of Salmonidaj and of the 
American shad, Alosa sapiclissima. It seems to me that the application of this measure 
deserves to be considered carefully. Let us suppose a river visited regularly by salmon 
for the purpose of spawning. If during the close season pisciculturists are permitted 
to catch a number of the spawning salmon in the river, strip them of their eggs and 
milt and hatch them in the most perfectly arranged hatchery, and then turn the fry at 
a certain stage again into the river, what wiU be the result ? If a greater percentage 
of eggs can be hatched under artificial conditions than under the natural, then of 
course the result will be to increase the number of fry produced in the river. 

This may be the case supposing that the eggs are preyed upon by other fishes or 
animals in the natural state, from which they are of course protected in the hatchery. 
But it would be equally effective to leave the eggs in the natural state and destroy 
their enemies. The artificially hatched fry are returned to the river soon after 
hatching, so that they are protected for a very short time, which, however, may be an 
advantage if in the natural state they are devoured in numbers when first hatched. Of 
course all this only applies to the case supposed. When artificially fertilised eggs or 
hatched fry, derived from other places, are put into a river, they will of course add to 
the sahnon population of the river if the conditions necessary for their life prevail iit 
that river. 

Considering now the case of the American shad, we find the problem different. The 
estuaries, when the American Fish Commission commenced operations, were over fished, 
and some had been entirely depopulated. There was no close season for shad, in fact it 
was scarcely possible to institute one, for the shad unlike the salmon enters the river 
only a very short time before it actually spawns, and the immense majority of 
individuals captured are, like the herrings taken in Britain, either actually rij^e or 
very nearly so. Hence a close season would have meant prohibiting the fishing 
altogether. Such numbers of shad were taken for many years, that the number of 
eggs deposited was not nearly sufficient to keep up the numbers of the species. Kearly 

u 



146 

all tlie ripe eggs and milt -which ought to have developed into the next generation were 
actually devoured by the people who ate the shad. The pisciculturists, under the 
direction of the Fish Commissioner, therefore first invented methods and apparatus by 
which the eggs of the shad could be artificially fertilised and hatched, and then they 
organised a system under which every year a large number of the ripe fish captured 
were stripped of their eggs and milt which were returned either to the same river or 
others in the form of healthy fry. The consequence is that now the estuaries on the 
Atlantic side of the United States yield annually a rich harvest of adult shad, and this 
valuable fishery is absolutely dependent on the piscicultural operations of the National 
Fish Commission. 

Let us now consider the case of the sole. Soles are captured without- intermission 
the whole year round, and their habitat is practically only coextensive with the 
trawling grounds. Soles do not, our knowledge enables us to infer with some 
certainty, migrate or travel about to any great extent. There may be of course 
distant areas where soles are abundant, but the existence of these is not sufficient to 
maintain the sole population of the extensive areas where they are constantly captured. 
Now I have shown that the artificial fertilisation and hatching of soles' eggs, though 
presenting unusual difficulties, is by no means impossible. It is almost impossible to 
interfere with trawling. Suppose that by further experiments it were shown that 
millions of soles' eggs could be artificially fertilised, hatched, and returned to the sea. 
It is evident that this would necessarily have the effect of increasing the supply of 
soles. For all these eggs would be procured from soles captured for the market, and 
would, if not artificially hatched, be devoured along with the soles themseh-es. Of 
course the expense of providing properly equipped hatcheries and mamtammg a staff 
of men who would collect the eggs and take care of them during development would 
be very large. But if this expense were provided from the public funds, some return 
for it would be received by the public in the form of more abundant and cheaper soles. 
Whether the national account on this item would result in an annual profit or an 
annual loss I am not yet prepared to say. 

On the other hand, it seems to me at least possible that the artificial fertilisation 
of the eggs would alone be sufficient, and that the artificial hatching in expensive 
hatcheries would be unnecessary. We have at present little reason to assume that, 
given a certain number of fertilised eggs more fry would be produced from them by 
hatching them in artificial apparatus than by placing them in the sea to develop under 
natural conditions. It is conceivable that the ripe females and males captured by the 
trawl during the spawning season should be stripped by a man on board a trawler, 
and the fertilised eggs so obtained should be simply thrown overboard. This would 
be a direct gain to the sole population of our seas, for every one of those eggs would, 
if not artificially fertilised, be sent to market inside the female soles and cooked. In 
fact ripe eggs are now cooked in the ovaries of soles in enormous numbers everj' 
spawning season. 



I 



147 

Of course much greater results would be effected by simplj- prohibiting the capture 
of soles at all from the middle of Februarj^ to the end of April ; but this could only be 
done by prohibiting trawling during those months, for in my opinion soles once 
captured in the trawl are usually too much injured to survive if again returned to the 
sea. I have shown that they do not survive when placed in our aquarium tanks {see 
p. 115). If trawling were prohibited who would compensate the fishermen and capitalists 
engaged in the business ? That would be more expensive than maintaining a national 
staff of pisciculturists to hatch soles' eggs. On the other hand, we must consider if it 
is possible under any imaginary system that there should be a mail on board every 
trawler capable of artificially fertilising the eggs of soles during the spawning period. 
It would scarcely be practicable to send out a trained pisciculturist in every trawler. 
It is possible, however, in imagination at least, that the skipper of every trawler should 
carry out the necessary operations, though it would probably be a long time before 
trawling skippers would possess the necessary knowledge or care sufficiently for the 
future. If such operations were expected of them they would have to be trained in 
practical pisciculture, and pass an examination in that subject as they are now 
required to pass in seamanship. 

I make no claim to originality in this idea. Years ago Professor Ewart, of the 
University of Edinburgh, who has identified himself with the piscicultural work of the 
Scottish Fishery Board, published the suggestion of a similar scheme to be applied to 
herrings. I believe it has never been carried out, and I doubt at present if such 
measures for maintaining the supph* of herrings are required. It has occurred to me to 
consider whether the same scheme might be applied to soles, and I think it quite pos- 
sible that Professor Ewart's suggestion may in the future lead to very important results. 

The only other possible methods of increasing the numbers of soles are to increase 
the supply of food or to diminish the numbers of the natural enemies of the sole. No 
practical means can be suggested by which the supply of food could be increased, but 
it might well be worth while to rigoi'ously destroy useless predatory fish which have no 
value themselves and which live entirely on valuable food fishes. At present trawlers 
constantly throw back anglers and dog-fishes into the sea alive after they have brought 
them on deck. I think it would be advisable that these fishes should be systematically 
killed before being returned to the sea, for if valuable fishes can be diminished in 
numbers the abundance of their enemies could be reduced also. 

There is not much to be said about the domestication of soles. It is certain that 
soles will live in captivity and grow to a large size. The Association is now making 
arrangements to keep young soles in a large piece of enclosed sea-water at Sheerness. 
But it is evident that the capture of young soles to be merely retained in captivitj- and 
killed when mature will not prevent the diminution of the numbers in the sea. If the 
adults were kept in captivity and their eggs taken and reared a new industry of sole- 
raising might be started, but it is doubtful whether this would compensate for the 
extermination of soles from the great trawling grounds. 



PLATES. 



Pl^AIE I. 

Drawing of a living Sole, lying on coarse bright-coloured gravel, in a shallow porcelain 
distil full of sea-uatei', and exposed to dajlight from a south window. 



*l 



Plate II. 

Dravying of the same specimen as that represented in Plate I lying on washed coal in 
a deep wooden luij and shaded from the light. 




00 

< 
o 

D 
> 

< 

LU 
_l 

o 

CO 



Plate III. 



Drawing of a living Sole, not the same specimen as represented in I'late I, lying in a 
shallow dish of while porcelain full of sea-water and exposed to strong day- 
light from a south wiudcw. 








"CO 



■X. 




m 






Li, 



Plate IV. 



Drawing of the specimen represented in Plate III on the day after its death. 




< 

o 

-J 

D 
> 

< 

u 

_) 

O 
CD 



II 



Plate V. 

The lower (left) side of the Common Sole. Two specimens of the parasite Phyllonella 
sulece are shown on the skin beliind the liead jusL below the lateral line. 



• 




00 

< 

o 

D 
> 

< 

_l 
O 
CO 



f\\ 



Platk VI. 

Fig. 1. The Lemon or Sand Sole {Solea lascaris), natural size. 

Fig. 2. Lower side of tlie head of llie same, showing the dilated anterior nostril. 



Plate VII. 

Fig. 1. The Thickback {Solea variegata), natural size. 

Fig. 2. Lower side of tlie head of the same. 

Fig. 3. The Solenette {Solea lutea), natural size. 

Fig. 4. Lower side of the same, 



> 

-I— 

a. 





V 



.'-. I. 



''. ,'+/ 



■ ,"« 


.-/^^f 


^^-.^. 


"■(?'• 




mj ' 







V-*.- 



z' 



V^- 



i 



N 



klii'ik' 



< 




f- 




< 

o 


< 

ID 


uu 


H 


Q:: 


..I 


< 




> 


< 




uu 


< 


-1 


UJ 


O 


J 


(f) 


o 




CO 


•^ 




t^ 


CNJ 


to 


•9 


tf) 


t— 


-OO 


in 


u. 


-o/) 




u. 





Plate VIII. 

Fiw. 1. The viscera of the female Common Sole in situ, natural size. 

Fiff. 2. The body cavity of the female Common Sole after all the viscera have been 
removed except the ovary and kidneys, which are left in situ. The wooden 
rod passes through the anus, the blue probe passes through the external 
aperture of the common oviduct up into the left ovary, the black bristle 
passes into the urinary bladder which lies beneath the oviduct. 



r^ 









4J 

.11 


■*^ 






2. 


*^ 







5 



o 

in 



.-a 

■CO 



o 
'o 




O 



Plate IX. 

Fi2- 1. Tlie viscera of the male Common Sole in situ, natural size. 

Fig. 2. The body cavity of the male Common Sole after all the viscera have been 
removed except the testes and kidneys, which are left in situ, natural size. 
The wooden rod passes through llie anus, the black bristle passes into the 
urinary bladder, which lies beneath the cords containing the testicular 
ducts. 








m 






•00 



o 






Plate X. 

Fig. 1. The skeleton of the Common Sole; the branchial arches, jaws, and bones of 
the paired fins have been removed, all the other bones are in their natural 
position in relation to one another. 

Fig. 2. One of the dorsal fin-rays : a. from the side ; b. from the front. 




i 

ex 

n 
3 



> 

o 
CO 



Pj^ati: X 



Fig. 1. The superficial bones of the right or iqiper side of the head of the Comiuon 
Sole. 

Fig. 2, The superficial bones of the left or lower side. 



Reference letters : — 



hm. 


hyomandibuliii 


mx, 


niesoptt'iT','oi<l 


int. 


metapterygoid 


m. 


mandible. 


PK 


pterysroid. 


pa, 


palatine. 


«. 


syniplectic. 



px, 

0, 

po, 
to, 
so. 



quadrate. 

maxilla. 

premaxilla. 

opercular. 

])reopercular. 

interopercular. 

snbopercular. 



Fig. 3. The bones of the branchial arches and paired fins, lateral view. 
Fig. 4. The bony branchial arches spread out and seen from the dorsal side. 



Reference letters and numbers 



14, 2ud epibraiichial. 

16, 2nd hypobranciiial. 

17, 3rd pliarynfTobrancliial. 

18, iJrd epibrauchial. 

19, 3rd ceratobraiichial. 
'20, 3rd hypobraiK-liial. 
21, 4th epibrancliial. 

25, post-temporal. 

26, supra-clavicular. 

27, clavicle. 

28, jugular. 

29, scapula. 

30, coracoid. 

31, pubic. 



Fig. 5. The skull, showing the separate bones and their sutures, from the right side. 
Fig. 6. The same from the left side. 
Fig. 7. The same from the dorsal side. 



hbl. 


1st basibranchial. 


U2, 


2ud ditto. 


hb3, 


3rd ditto. 


hh. 


basihyal. 


hh, 


hypohyals. 


ch. 


ceratohyal. 


cbl. 


1st cerato-branchial. 


cb2, 


2nd ditto. 


IP^ 


lower pharyngeal. 


np, 


upper pharyngeal. 


•> 


styluhyal. 


3! 


epihyal. 


8, 


1st pliarj-ngobranchial. 


9, 


1st epibrancliial. 


11, 


1st hypobranchial. 



Fig. 8. The posterior surface. 
Reference letters : — 



h.o. 


basioccipifal. 


s.o. 


supraoccipital 


e.x.o. 


exoccipital. 


ep.o. 


epiotic. 


pt.o. 


pt erotic. 


op.o. 


opisthotic. 


pr.o. 


prootic. 


sp.o. 


sphenotic. 



jia. parietal. 

l.f. left frontal 

r.f. right fiontf.l. 

pa.s. parasphenoid. 

vo. vomer. 

■tnes.e, mesethmoid. 

r.ect.e. right cctethiuoid 

l.ect.e. left ditto. 



iilll 



Plate X 



Firr. 1. The superficial bones of tlie riglit or upper side of the head of the Common 
Sole. 

Fig. 2, The superficial bones of the left or lower side. 

Eeference letters : — 



A III . 


hjoniandibular. 


}rut. 


mcsopterygoid. 


ml. 


metapterj-goift. 


in. 


mandible 


pt. 


ptciyaroid. 


pa, 


palatine. 


»'• 


syraplectic. 



2. 


(luadratc. 


,c, 


maxilla. 


px, 


prcma.xilla. 


0, 


opercular. 


po, 

10, 

so. 


prcopercular. 

interopcrcular 

snbopercular. 



Fic 3. The bones of the branchial arches and 
Fig. 4. The bony branchial arches spread out 
Eeference letters and numbers : — 



paired fins, lateral view. 

and seen from the dorsal side. 



14, 2nd cpibrancliial. 

16, 2nd hypobrancliial. 

17, 8rd pliaryngoliraiicliial. 

18, 3rd cpibrancliial. 

19, 3rd ccratobrancliial. 

20, 3rd hypobrancliial. 

21, 4tli epibrancliial. 

25, po.st-temporal. 

26, supra-clavicular. 

27, clavicle. 

28, jugular. 

29, scapula. 

30, coracoid. 

31, pubic. 



Fig. 5. The skull, showing the separate bones and their suiures, from the right side. 
Fig. 6. The same from the left side. 
Fig. 7. The same from the dorsal side. 
Fig. 8. The posterior surface. 



661, 


1st basibranchial. 


66 2, 


2nd ditto. 


66 3, 


3rd ditto. 


bh, 
hh, 
ch. 


basihyal. 

liypob}-aIs. 

ceratoliyal. 


chl. 


1st cerato-branchial. 


cb2, 


2nd ditto. 


Ip, 


lower pharyngeal. 


up, 
•2, 


upper pharyngeal. 

stylobyal. 


■\ 


epihyal. 


s. 


1st pliaryngobranchial 


!», 


1st e[iibrancliial. 


ll, 


Ist hypobrancliial. 



Eeference letters : — 

6.0. basioccipital. 

s.o. supi-aoccipital. 

e.x.o. exoccipital. 

ep.o. epiotic. 

pl.o. pterotic. 

op.o. opisthotic. 

pr.o. prootic. 

sp.o. spbenotic. 



jia. parietal. 

l.f. left frontal. 

r.f. right fi-ontf.l. 

pa.s. paraspbcnoid. 

vo. vomer. 

men.e. uiesethmoid. 

r.ect.c. right cctethnioid. 

l.cct.c. left ditto. 



Plate XI 




jjr o. 



pro 



J.T. Curainghamdil 



Solea vulgaris 



L]th£>Inip CBmb Sci !• 



Plate XII. 

General view of the niusculaturs of the Coimuou Sole seen from the right side, after 
removal of the skin. The superficial abductors of the ventral fm have been 
removed, to expose the elevators and depressors of the ventral fin-rays which 
lie beneath tliem ; the same dissection has been made along the anterior 
fourth of the dorsal fin. 






i 





sssg^.. 







g 

3 



id 

> 

<u 
■q 
en 



rhAiF. XIII. 

Fig. 1. Transverse section of the right ovary of a young Common Sole, 7^ inches long, 
killed May 2, 1889 ; magnified 45 times, linear. 

f.e. fibrous tissues forming the wall of the ovary. 
o.g. ovigerous lamellie. 
hx. blood-vessels, ovarian artery and vein. 

Fig. 2. Portion of an ovigerous lamella from transverse section of an ovarv of a Sole 
10^ inches long, killed January 26, 1889 ; magnified 450 times. 

ff.e. germinal epithehuni. 
(). ova. 

Fig. 3. Section of an ovum approaching maturity, from the ovary of a Sole killed 
when spawning was almost finished, on April 1 1, 1889 ; magnified 70 times. 

h.v. blood-vessels. 
f.e. follicular epithelium. 
f.m. follicular membrane. 
v.m. vitelline membrane. 

Fig. 4. Transverse section of the right testis of a Sole 9 inches long, immature ; 

magnified 45 times. 

f.e. fibrous envelope. 

r.t. radial testicular tubes. 

Li. longitudinal testicular tubes. 

Fijf. 5. Closed end oi one of the radial testicular tubes shown in Fig. 4 : magnified 450 

times. 

f.e. fibrous envelope. 

ij.c. male germinal epithelium. 

Fig. ha. Longitudinal portion of a testicular tube from the same section cut 
transversely, containing spermatoblasts and ripe spermatozoa ; magnified 
450 times. 

Fig. 6. Transverse section of the cord containing the testicular ducts from an adult 
male Sole killed in the breeding season, March 28, 1889; magnified 70 
times. 

f.t. fibrous tissue. 

l.t. the testicular ducts. 

u.h. urinary bladder lined by an epithelium. 

Fig. 7. Spermatozoon of Dab [Tleuronectes limandoC) ; magnified 500 times. 




^ 



t^ 









/. 












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ir 



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^^ 






Plate Xlll 



.1 







f'U--' 



/e. 



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.fr> 



■■<£i & 








;.«. 



V 




f.e.. 



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t^^ 



f 



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5a. 




/ 



J T '.lunninghiTT; del 



3oiea vulgaris 



Lithiimp Camb ScilnttCo 



il 



Ji 



I 



Plate XIV. 

Fig, 1. Scale of Common Sole from middle of body ; magnified. 

Fig. 2. One of the lateral line scales of the same. 

Fig. 3. Scale of Thickback. 

Fig. 4. Scale of Lemon or Sand Sole. 

Fig. 5. Scale of Solenette. 

Fig. G. PhyJIonella solece, the parasite from the skin of the Common Sole ; magnified. 

l^s. i)osterior sucker. 

p. aperture for the penis. 

u. aperture of the uterus. 
n.g. anterior glandular areas. 

Fig 6a. Egg of same, magnified 100 times. 

Fig. 7. Ideal longitudinal section of the skin along the lateral line of the Common Sole ; 
magnified 70 times. 

ep. epidermis. 

c. chromatophores. 
d.t. dermal tube. 
s.c. scale in section. 

/. fibrous tissue of the derma with areolar tissue in spaces. 

J), external pores. 
s.o. sense organ. 

11. nerve. 



II 



Plate XIV 






ti "' 



:^" 



'i-.. 



' — r 



9.. 



■'3£--^:. 






J T. Cunningham. del 



Solea vulgaris 



: i^.L'amb.Sc: InstC'c 



I 



II 



Plate XV. 



Fig. 1. Sectiun of a portion of the skin of the lower side of head of the Common 
Sole ; magnified 70 times. Reference letters as in Fig. 7, PI. XIV, with 
the addition of /"/, tactile filaments. 

Fig. 2. Lower side of the head of the Sole dissected to sliow the cutaneous nerves : 
natural size, 

V 2. Maxillary branch of the 5th. 
V 2 a. palato-nasal branch of 5th. 

V 2. mandibular branch of 5th. 
VII 1. mandibular branch of 7th. 
VII 2. hyoidean branch of 7th. 

VII 2 a. opercular branch of 7th. 
X 6 a. supra-temporal branch of vagus. 
X 6 Z*. another anterior branch of the vagus. 

Fig, 3. Egg of Cominon Sole taken in tow-net in Mount's Bay, March 1, 1SS9. 
Magnified 45 times, hi. blastoderm, y.s. yolk segments, o.(j. oil globules. 

Fig. 4. An egg of the same, artificially fertilised, March 23, 7 a.m. ; drawn March 24, 
5 p.m.; same magnification. 

Fig. 5. An egg of the same, artificially fertilised, March 23, 7 a.m. ; drawn March 25, 
12 noon ; same magnification. 

Fig. ti. An egg, fertilised artificially. April 12, 188'J ; dranw April 15, 4 p.m. 
Both black and coloured pigment cells present, the latter green by reflected 
light; e. eye, m.s. mesoblastic somites. 



Plate XV 













J r Cunnjngham.del 



SoJea vulgaris 



Plate XVI. 



Fig. 1. Egg of Common Sole, artificially fertilised, April 12,1889, 10 a.m.; drawn 
April 15, 4 p.m. Magnified 45 times; same stage as that shown iu PI. XV, 
Fig 6, in profile, o.g. oil globules. 

Fig. 2. An egg of same taken in tow-net off Plj-month (near the Mewstoue), March 29, 
1889; drawn March 30 ; same magnification, e. eye. _?/L yolk. 



Fig. 3. Larva of same taken 4 m. south of the Mewstone, March 30, 1889; right 
side ; magnified 35 times, yk. yolk. cm. auditory organ, na. nasal capsule. 



o* 



Fig. 4. Larva of same, hatched March 28, from egg taken off Penlee Point, March 27, 
left side ; magnified 35 times, ht. heart, pt. pectoral fin. int. intestine. 

Ficr. 5. Young Common Sole | inch long, taken in Mevagissey Harbour, May 15, 
1889 ; magnified S| times. 

Fig. 6, Egg of I he Thickback {Solea vanegata), taken in tow net S. of the Eddystone ; 
drawn April 21, 1889; magnified 45 tunes. 



PhthXVI, 




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^•\!^ ;?v 



^^ •v^;^-li^:-*V.. ,■■■ 



,••'. fti 



>K-y*:^-A' 






•^ 



ri^>^^ -■'■ 




Fi<^ 1-5 SOLEA VULGARIS F.6 fi Sni FA vji 



Tlate XVII. 



Fig. 1. Larva of Thickback newly hatched, April 24, 1889; magnilied 35 times. 
Pigment as seen by reflected light, yk. yolk. 

Fig. 2, Larva of same two days after hatching, April 23, 1889. Same magnification 
2^. pectoral fin. Jd. heart. 

Fig. 3. Larva of Flounder {Pleibronectes flesus), two days after hatching, February 20, 
1889, from egg artificially fertihsed ; magnified 35 times. 

Fig. 4. Larva of same six days after hatching, February 24, 1889, from the same 
lot as the preceding ; same magnification. 

Fig. 5. Young Flounder taken in Mevagissey Harbour, April 2, 1889 ; drawn K])v\\ 5 ; 
nuignified about IS times. 



ri.ilrXVIf. 



pi 



4a^:' 



hi 



t-m ' n ' 



; o^ ' o . . 



j?f 




SOLEA VARIECATA 



"ti-j 




PLEURONF.CTES FLESUS 





-: ^v-;^:V, • 



m 



PLEURON'ECTES 



Fio. 1.2. SOLEA VARIECATA. Fi,.|. 3 5. PLEURONECTES FLESUS 



Plate XVIIL 



Fi". 1. Young 'Floundev {Pleuro7iectcs fesus) taken h\ Mevagissey Harbour, April 2, 
1889 ; magnified about 14i times, pv. pelvic fin. 



Fig. 2. Larva of Dab {Pleuronectes limanda) newly hatched, from artificially fertilised 
egg, March 11, 1889 ; magnified 35 times, pt. pectoral fin. yk. yolk. 

Fig. 3. Larva of Merry Sole {Pleuronectes viicrocephalm), March 25, 1889, four days 
after hatching, from artificially fertilised egg ; same magnification. /. liver. 
ht. heart. 

Fig. 4. Larva of Plaice {Pleuronectes platessa), February 27, 1889, five days after 
hatching, from artificially fertilised egg; same magnification, a. anus. 
nch. notochord. 

Fig. 5. Young Brill {JUinnihits Icinns) taken at surface of water in Sutton Pool, June 1, 
1889 ; natural size. 







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PRINTERS IN ORDINARV TO HEK MAJESTY, 

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SMITHSONIAN INSTITUTION LIBRARIES 

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